Class 10 Physics

Haryana Board Class 10 Physics Solutions For Chapter 4 Magnetic Effects Of Current Multiple Choice Questions And Answers

Question 1. A student learns that the magnetic field strength around a bar magnet is different at every point. Which diagram shows the correct magnetic field lines around a bar magnet?

Answer: 3.

Question 2. A student places some iron fillings around a magnet. The iron fillings arrange themselves as shown in image.

The student labelled four different regions around the magnet. Where would be the magnetic be the strongest?

1. P
2. Q
3. R
4. S

Answer: 3. R

Question 3. A student placed a magnetic compass around a straight current carrying wire. The student noticed when he moved the compass away from the wire, the deflection in compass decreases. How would be the magnetic field lines around the conductor?

Answer: 2.

Question 4. The image shows the magnetic field lines around a straight current-carrying conductor.

If the direction of the current in the straight wire is changed, what change in the magnetic field line will be observed?

Answer: 1.

Question 5. Which diagram shows the magnetic field lines around a current-carrying circular loop?

Answer: 2.

Question 6. Which diagram shows the correct direction of the magnetic field lines at point P and Q in current carrying circular loop?

Answer: 2.

Question 7. The magnetic field lines of solenoid are similar to the magnetic field lines of bar magnet. Which image correctly shows the solenoid as a bar magnet?

Answer: 3.

Question 8. Where should the magnetic compass be placed in solenoid to get maximum deflection in the magnetic compass?

Answer: 3.

Question 9. The image shows Fleming’s left-hand rule.

Which option explains the rule to understand the working of the motor?

1. When a current-carrying conductor is moved with a force, it creates a magnetic field.
2. When a conductor is moved inside a magnetic field, current is produced in the conductor.
3. When a magnetic field is moved relative to the conductor, current is produced in the conductor.
4. When a current carrying conductor placed in a magnetic field, it experiences a force by magnetic field.

Answer: 4. When a current carrying conductor placed in a magnetic field, it experiences a force by magnetic field.

Question 10. A metal rod PQ. is placed in the magnetic field. The ends of the rod are connected with a battery using wires.

Where will the rod move?

1. Upward
2. Downwards
3. Into the field
4. Out of the field

Answer: 4. Out of the field

Question 11. A student inserts a bar magnet in the coil. The student observes deflection in the galvanometer connected to the coil. What will happen if the magnet is continuously getting in and out of the coil?

1. The current induced in the coil will increase
2. The current will change its direction continuously
3. The magnetic field will create a motion in the coil
4. The magnetic field of the bar magnet would keep decreasing

Answer: 2. The current will change its direction continuously

Question 12. A student makes an arrangement to study electromagnetic induction, as shown.

She changes the arrangement in four different ways.

In which trial would the galvanometer remain undeflected?

1. Trial 1
2. Trial 2
3. Trial 3
4. Trial 4

Answer: 4. Trial 4

Question 13. The image shows the components of an electric generator.

When the coil PQRS is rotated as shown. What is the direction of electric current when coil completes half cycle of the rotation?

Answer: 2.

Question 14. Appliances that have a metal body are generally connected to the earthing wire. What is the reason to earth these wires?

1. To prevent an excess of current
2. To prevent the leakage of current
3. To provide extra current to appliance
4. To provide high resistance to the appliance

Answer: 2. To prevent the leakage of current

Question 15. Which diagram shows the domestic electric circuit?

Answer: 4.

Chapter 4 Magnetic Effects Of Current Very Short Questions And Answers

Question 1. Why does a compass needle show deflection when brought near a current carrying conductor?

Answer: The magnetic field is produced around the current carrying conductor.

Question 2. Positively charged particles moving towards the west are deflected towards the north by a magnetic field. What will be the direction of the magnetic field?

Answer: Upward direction in accordance with Fleming’s left hand rule.

Question 3. If you hold a coil of wire next to magnet, no current will flow in the coil. What else is needed to induce a current?

Answer: Relative motion between the coil and the magnet.

Question 4. What is the qualitative effect of inserting an iron core into a current-carrying solenoid?

Answer: Magnetic field becomes very strong.

Question 5. How is the magnetic field inside the long solenoid carrying current?

Answer: The Magnetic field is uniform inside the long solenoid carrying current.

Question 6. Name the rule for finding the direction of the magnetic field produced by a straight current-carrying conductor.

Answer: Maxwell’s right-hand thumb rule.

Question 7. What is the shape of a current-carrying conductor whose magnetic field pattern resembles that of a bar magnet?

Answer: Solenoid

Question 8. A circular conducting coil has ‘n’ turns. If the magnitude of the magnetic field produced by a single coil is B, then what is the magnetic field of the entire coil?

Answer: Since the magnetic field produced by current-carrying wire at a given point depends directly on the current passing through it. Therefore, if there is a circular coil having “n” turns, the field produced is “n” times as large as that produced by a single turn. This is because the current in each circular turn has the same direction, and the field due to each turn then just adds up.

Question 9. A soft iron bar is enclosed by a coil of insulated copper wire as shown in the figure. When the plug of the key is closed, then where would the face B of the iron bar be marked?

Answer: N-Pole

Chapter 4 Magnetic Effects Of Current Short Questions And Answers

Question 1. For the coil in the diagram below, when the switch is pressed:

1. What is the polarity of end A?
2. Which way will the compass point then?

Answer:

1. End A becomes the S-pole because current flows in a clockwise direction at A.
2. When A becomes S-pole, the other end becomes N-pole. So, the tip of the compass (which also has North polarity) moves away from this end i.e., the tip moves towards the right.

Question 2. What, according to Maxwell’s Right Hand Thumb rule, will be the direction of the current when lines of the magnetic field are in the anti-clockwise direction?

Answer:

The current will be flowing in the upward direction when the direction of the magnetic field is in the anti-clockwise direction.

Question 3. The figure given below shows the magnetic field between two magnets:

1. Label the other poles of the magnets.
2. Which is the weaker magnet?

Answer:

Magnet 2 is weaker.

Question 4. What are the two ways in which you can trace the magnetic field pattern of a bar magnet?

Answer:

1. By using iron filings
2. By using compassion

Question 5. Copy the figure below which shows a plotting compass and a magnet. Label the North pole of the magnet and draw the field line on which the compass lies.

image

Answer:

image

Question 6.

1. Mention the factors on which the direction of force experienced by a current-carrying conductor placed in a magnetic field depends.
2. A proton beam is moving along the direction of a magnetic field. What force is acting on the proton beam?

Answer:

1. The direction of the force exerted on experienced by a current carrying conductor mainly depends on the two factors:
   • The direction of the current , the direction of flow of positive charge determine the direction of the force as described by the Flemings left hand rule,
   • The direction of the magnetic field; the force exerted on the conductor depends on the orientation of the magnetic field. This is also defined according to the Flemings left hand rule,
2. As the proton beam is moving along the direction of the magnetic field it will experience no force. The strength of the magnetic field depends on the orientation of the conductor in the magnetic field.

It experiences maximum force when the direction of flow of current and the magnetic field is perpendicular to each other i.e. the angle between the two is, let’s say θ = 90° as shown in the figure (2). If the direction of the current and the magnetic field is parallel i.e. θ = 0° as shown in the figure (1), the conductor will experience no force.

image

Question 7. What are the three factors which cause a change in magnetic flux of the coil?

Answer:

Changes in the magnetic flux of a coil occur due to:

1. Relative motion between a coil and a magnet placed near it.
2. Relative motion between a coil and a current-carrying conductor placed near it.
3. Change of current in the conductor placed near the coil.

Question 8. The diagram below shows a bar magnet surrounded by two compasses numbered 2 and 4. What directions will these compasses show?

image

Answer:

Directions shown by the needle of compasses 2 and 4 would be as shown below.

image

This is because the magnetic field lines arise from the North Pole and end at the South Pole.

Question 9. A simple motor is made in a school laboratory. A coil of wire is mounted on an axle between the poles of a horseshoe magnet, as illustrated.

image

In the example above, coil ABCD is horizontal and the battery is connected as shown.

1. For this position, state the direction of the force on the arm AB.
2. Why does the current in the arm BC not contribute to the turning force on the coil?

Answer:

1. Downwards
2. Because BC is in the same direction as the direction of field lines. Force is minimum when the direction of current in the conductor is the same as that of the magnetic field. BC will not contribute as the force on this part of the coil will be cancelled by the force on DA.

Question 10. Geeta performed an activity in the school laboratory to observe the effects of magnetic field lines. Based on her observation, she has drawn the magnetic field lines of two magnets as shown in fig. 1 and fig. 2.

image

1. Select the figure that represents the correct pattern of field lines. Give reasons for your answer.
2. Also, name the poles of the magnets facing each other.

Answer:

1. Figure B represents the correct pattern of field lines. In figure A, field lines cross each other which is not possible because if they cross each other, at the point of intersection, there would be two directions of field lines,
2. In figure B, field lines are emerging in nature, so poles of magnet facing each other are north poles while opposite faces will have south polarity.

Question 11. A student drew three magnetic field lines 1, 2 and 3 of a bar magnet with the help of a compass needle as shown in the figure.

image

Is this configuration possible? If not, then what is wrong in the given figure and why?

Answer:

No, this type of configuration is not possible as:

Two field lines cannot intersect each other,

Direction of field line as it emerged from south pole and merged at north pole. ‘3’ is wrong as, it emerged from south pole and merged at north pole.

Question 12.

1. What are the patterns formed by the circular loop carrying current?
2. Which rule is used to find the direction of the magnetic field produced due to the electric current in a circular loop?
3. On which factors does the strength of a magnetic field depend?

Answer:

1. The circular loops carrying current forms concentric circular patterns of the magnetic field due to electric current.
2. The direction of the magnetic field of the loop carrying current can be determined by the clock face rule.
3. The strength of the magnetic field due to current depends on the
   1. Number of turns of wire in the coil
   2. Radius of the coil
   3. Current flowing in the coil.

Question 13. How does the strength of the magnetic field at the centre of a circular coil of a wire depend on?

1. Radius of the coil
2. Number of turns of wire in the coil
3. Draw the magnetic lines of force in case of a circular coil of wire

Answer:

1. The strength of the magnetic field (B) is inversely proportional to the radius of the circular loop (r).
2. The strength of the magnetic field (B) is directly proportional to the number of turns in the coil (N).
3. The magnetic field lines will be as shown below.

image

Question 14. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is held stationary inside the coil?

Answer:

When a bar magnet is held stationary inside the coil, there will be no deflection in the galvanometer indicating that no current is produced in the coil.

Question 15.

1. If a current carrying straight conductor is placed in east-west direction, then find the direction of the force experienced by the conductor due to earth’s magnetic field.
2. Mona draws magnetic field lines of field close to the axis of a current carrying circular loop. As she moves away from the centre of the circular loop she observes that the lines keep on diverging. How will you explain her observation?

Answer:

1. The force will act in upward direction perpendicular to both, the direction of current as well as to the field. The direction of force experienced by the conductor gets reversed, i.e., in the downward direction.
2. Strength of the magnetic field decreases as distance increases. This is indicated by the decrease in degree of closeness of the lines of field.

Question 16. A magnetic field is described by drawing the magnetic field lines. When a small north magnetic pole is placed in the magnetic field created by a magnet, it will experience a force. And if the North Pole is free, it will move under the influence of the magnetic field. The path traced by a north magnetic pole free to move under the influence of a magnetic field is called a magnetic field line.

image

Since the direction of magnetic field line is the direction of force on a north pole, so the magnetic field lines always begin from the N-pole of a magnet and end on the S-pole of the magnet. Inside the magnet, however the direction of magnetic field lines is from the S-pole of the magnet to the N-pole of the magnet. Thus, the magnetic field lines are closed curves. When a small compass is moved along a magnetic field line, the compass needle always sets itself along the line tangential to it. So, a line drawn from the south pole of the compass needle to its north pole indicates the direction of the magnetic field at that point.

1. Do the magnetic field lines intersect? If not, why?
2. A strong bar magnet is placed vertically above a horizontal wooden board. What would be the magnetic lines of force?
3. Where do we use Magnetic field lines?

Answer:

1. No two magnetic field lines are found to cross each other. If two field lines crossed each other, it would mean that at the point of intersection, the compass needle would point in two directions at the same time, which is not possible.
2. The magnetic field and hence the magnetic line of force exist in all the planes all around the magnet.
3. The relative strength of the magnetic field is shown by the degree of closeness of the field lines and the direction of the magnetic field is obtained by the tangent to the field lines at the point of intersection.

Question 17. Diagram below shows a circuit containing a coil wound over a long and thin hollow cardboard tube.

image

1. Show the polarity acquired by each face of the solenoid.
2. Draw the magnetic field lines of force inside the coil and also show their direction.

Answer:

1. The polarity acquired by the two ends is as shown below. (A shows North and South polarity).

image

Question 18. Identify the poles of the magnet in the given figures:

image

Answer:

1. Field lines emerge from north pole (N) and merge at the south pole (S) in figure (1), So the poles of the magnet are:

image

2. Field lines emerge from north pole (N) and merge at the south pole (S) in figure (2), So the poles of the magnet are:

image

Question 19. Richa is performing an experiment on magnetism for which she has used two magnets A and B. She felt that there was an attraction between the magnets. So, she drew the magnetic field lines as below.

image

But her teacher said that the diagram was wrong.

1. Why was the diagram wrong?
2. Draw the correct diagram.
3. What does the direction of thumb indicate in the right-hand thumb rule. In what way this rule is different from Fleming’s left-hand rule?

Answer:

1. From the drawing of Richa it is clear that the magnetic north poles are facing each other. But there was an attraction between the magnets. So, north pole of one magnet was facing the south pole of the other magnet.

2. The correct diagram is either of the two diagrams shown below:

image

3. In the right-hand thumb rule the r thumb indicates the direction of current in the straight conductor held by curled fingers, whereas in Fleming’s left-hand rule the thumb gives the direction of force experienced by current-carrying conductor placed in an external magnetic field.

Chapter 4 Magnetic Effects Of Current Long Questions And Answers

Question 1. Is the magnetic field same all around a bar magnet? Explain with reasons.

Answer:

No, magnetic field strength varies at every point around it. Magnetic field strength depends on the number of field lines per unit area.

If the field lines per area is more, then the magnetic strength in that area is strong, and if the field lines per area is less, then the magnetic strength is weak.

As the magnetic field lines per unit area is maximum at the poles, the magnetic strength is also maximum in that region.

Question 2. PQ is a current-carrying conductor in the plane of the paper as shown in the figure below.

image

1. Find the directions of the magnetic fields produced by it at points R and S.
2. Given r1 > r2, where will the strength of the magnetic field be larger? Give reasons.
3. If the polarity of the battery connected to the wire is reversed, how would the direction of the magnetic field be changed?
4. Explain the rule that is used to find the direction of the magnetic field for a straight current-carrying conductor.

Answer:

1. The magnetic field lines are produced is into the plane of the paper at R and out of it at S.
2. Field at S > Field at P The Magnetic field strength for a straight current-carrying conductor is inversely proportional to the distance from the wire.
3. If polarity is reversed, the current will go from top to bottom in the wire and the magnetic field lines goes in the clockwise direction on the plane which is perpendicular to the wire carrying current,
4. According to the Right-Hand thumb rule, the thumb is aligned to the direction of the current, and the direction in which the fingers are wrapped around the wire will give the direction of the magnetic field.

Question 3. An insulated copper wire wound on a cylindrical cardboard tube such that its length is greater than its diameter is called a solenoid. When an electric current is passed through the solenoid, it produces a magnetic field around it. The magnetic field produced by a current-carrying solenoid is similar to the magnetic field produced by a bar magnet. The field lines inside the solenoid are in the form of parallel straight lines. The strong magnetic field produced inside a current-carrying solenoid can be used to magnetise a piece of magnetic material like soft iron when placed inside the solenoid. The strength of the magnetic field produced by a current-carrying solenoid is directly proportional to the number of turns and the strength of the current in the solenoid.

1. What would be the strength of the magnetic field inside a long current-carrying straight solenoid?
2. By using which rule we can find the north-south polarities of an electromagnet?
3. A long solenoid carrying a current produces a magnetic field B along its axis. If the current is double and the number of turns per cm is halved, then what will be the new value of magnetic field?
4. A soft iron bar is enclosed by a coil of insulated copper wire as shown in figure.

image

When the plug of the key is closed, then where would the face B of the iron bar be marked?

Answer:

1. Magnetic field inside an infinite solenoid is uniform. Hence it is same at all points.
2. Clock face rule
3. For a long solenoid, magnetic field B oc In; where I is the flowing current and n is number of turns per unit length in the solenoid. Therefore, in the given case magnetic field will remain unchanged.
4. N-pole.

Question 4.

1. An induced emf is produced when a magnet is plunged into a coil. On which factor or factors does the magnitude of induced emf depend?

2. The wire in the figure below is being moved downwards through the magnetic field, so as to produce an induced current.

image

• What would be the effect of using a stronger magnet?
• What would be the effect of holding the wire still in the magnetic field?

Answer:

1. The number of turns of the coil, the speed with which the magnet is moved, and the strength of the magnet.

• The magnitude of the induced current increases.
• The induced current is zero.

Question 5. When a current is passed through the circular loop of wire, the magnetic field lines near the coil are nearly circular and concentric. At the centre of the circular loop, the magnetic field lines are straight. The strength of the magnetic field produced by a current-carrying circular coil (or circular wire) depends on:

1. Radius of the circular coil.
2. Number of turns of wire in the circular coil. The direction of the field lines can be found by applying the Right-Hand Thumb Rule.

image

• A long horizontal power line is carrying a current of 100 A in the east-west direction. What is the direction of the magnetic field at a point 1.0 m below it?
• What type of curve we get, between magnetic field and distance along the axis of a current-carrying circular coil?

Answer:

1. The current flows in the east-west direction. From the right-hand rule, we get the direction of the magnetic field as from north to south. The direction of the magnetic field will be the same at every point below the power line.
2. At smaller distances, the magnetic field will be described by concentric circles around the wire. As the distance increases, the circles become larger and larger. At the centre of the loop or coil, the magnetic field will appear as a straight line.

Haryana Board Class 10 Physics Solutions For Chapter 3 Electricity Multiple Choice Questions And Answers

Question 1. A charge of 100 C flows through a bulb in 5 minutes. How much current is flowing through the bulb?

1. 500 A
2. 100 A
3. 20 A
4. 0.3 A

Answer: 3. 20 A

Question 2. A conducting wire carries 1021 electrons in 4 minutes. What is the current flowing through the wire?

1. 40 A
2. 7 A
3. 4 A
4. 0.7 A

Answer: 4. 0.7 A

Question 3. Work of 14 J is done to move 2 C charge between two points on a conducting wire. What is the potential difference between the two points?

1. 28 V
2. 14 V
3. 7 V
4. 3.5 V

Answer: 3. 7 V

Question 4. In order to move a charge of 3 C between two points on a conducting wire, 12 J of work is done. How much increase or decrease in the voltage will increase the work done on the same amount of charge to 36 J?

1. -12 V
2. -8 V
3. +8 V
4. +12 V

Answer: 3. +8 V

Question 5. A circuit has a charge of 2C moving through it in 3 s. Which electrical component in the circuit, if present, will show the current?

1. Voltmeter will show a current of 6 A.
2. Ammeter will show a current of 0.7 A.
3. Rheostat will show a current of 0.7 A.
4. Resistor will show a current of 0.35 A

Answer: 2. Ammeter will show a current of 0.7 A.

Question 6. The image shows a circuit diagram.

What is being measured using the voltmeter?

1. Current in the circuit
2. Voltage in the circuit
3. Voltage across the resistor
4. Resistance offered by the resistor

Answer: 3. Voltage across the resistor

Question 7. What is the relationship between resistance and current?

1. They are directly related to each other.
2. They are inversely related to each other.
3. The resistance has a greater magnitude than current.
4. The current has a greater magnitude than resistance.

Answer: 2. They are inversely related to each other.

Question 8. Which plot shows the change in voltage when the current is gradually decreased across a resistor?

Answer: 1.

Question 9. Which one among a bar of an alloy of mass 2 kg and a 3 kg iron bar of same dimension has greater resistivity?

1. An iron bar because it has a higher mass,
2. Alloy bar because it has lower mass.
3. Iron bar because it has the same types of atoms,
4. Alloy bar because it has different types of atoms.

Answer: 4. Alloy bar because it has different types of atoms.

Question 10. A piece of wire is measured to have resistivity in the order of 1019 Ω m. What should its material be classified into?

1. Alloys
2. Insulators
3. Good conductors
4. Poor conductors

Answer: 2. Insulators

Question 11. Which combination of a 2 Ω resistor and 4 Ω resistor offers the least resistance to current in the circuit?

1. Series combination, which results in a net resistance of 2Ω.
2. Parallel combination, which results in a net resistance of 2Ω.
3. Series combination, which results in a net resistance of 1.5Ω.
4. Parallel combination, which results in a net resistance of 0.5Ω.

Answer: 4. Parallel combination, which results in a net resistance of 0.5.

Question 12. The image shows a combination of 4 resistors

What is the net resistance between the two points in the circuit?

1. 0.5 Ω
2. 1.0 Ω
3. 1.5 Ω
4. 2.0 Ω

Answer: 2. 1.0 Ω

Question 13. How much more heat is produced if the urrent is doubled?

1. Twice the original amount
2. Thrice the original amount
3. Four times the original amount.
4. Five times the original amount.

Answer: 2. Thrice the original amount

Question 14. A bulb has a resistance of 5. If 2 A of current at 200 V flows through the bulb, how much heat is produced by the bulb in 10 minutes?

1. 2.0 x 105 J
2. 4.0 x 105 J
3. 1.2 x 106 J
4. 2.4 x 106 J

Answer: 4. 2.4 x 106 J

Question 15. In order to reduce electricity consumption at home, what kind of appliance should one purchase?

1. One which draws low power
2. One which produces less heat
3. One which operates at a higher voltage
4. One which draws a high amount of current

Answer: 1. One that draws low power

Question 16. An electric toaster has a power rating of 200 W. It operates for 1 hour in the morning and 1 hour in the evening. How much does it cost to operate the toaster for 10 days at Rs 5 per kW h?

1. Rs 20
2. Rs 400
3. Rs 5000
4. Rs 10000

Answer: 1. Rs 20

Chapter 3 Electricity Very Short Answer Questions

Question 1. What is meant by saying that the electric potential at a point is 1 volt?

Answer: Electric potential at a point is 1 volt means 1 joule of work is done in moving lunit positive charge from infinity to that point.

Question 2. The potential difference across the wire having fixed resistance is tripled. By how much does the electric power increase?

Answer: P = V²/R = (3V)²/R; P = 9P

Question 3. What is the commercial unit of energy?

Answer: Kilowatt-hour

Question 4. What is the relation between the resistance (R) of the filament of a bulb, its power (P), and a constant Voltage (V) applied across it?

Answer: P = V²/R

Question 5. What is the general name of the substances having infinitely high electrical resistance?

Answer: Insulators

Question 6. How is an ammeter connected in a circuit to measure the current flowing through it?

Answer: An Ammeter is connected in series in an electric circuit.

Question 7. Calculate the current in the circuit if 40 C of charge is passed through a point in 10 seconds.

Answer: I = Q/t = 40/10 = 4A

Question 8. State whether a voltmeter has a high resistance or a low resistance. Give a reason for your answer.

Answer: Voltmeter has a high resistance so that it takes a negligible current from the circuit.

Question 9. If the current in a wire is flowing in the vertically downward direction and a magnetic field is applied from west to east, what is the direction of the force on the wire?

Answer: According to Fleming’s left-hand rule direction of the force will be in the South direction.

Question 10. State whether an electric heater will consume more electrical energy or less electrical energy per second when the length of its heating element is reduced.

Answer: The electric heater will consume more electrical energy when the length of its heating element is reduced because resistance is directly proportional to length (R = ρ/ I x A ). Hence, resistance will decrease. Power is inversely proportional to resistance (P = V²R ) . Hence, power will increase.

Question 11. Define one coulomb charge.

Answer: One coulomb of charge is that quantity of charge which exerts a force of 9 x 109 Newton on an equal charge is placed at a distance of 1 m from it.

Question 12. A car headlight bulb working on a 12 V car battery draws a current of 0.5 A. The resistance of the light bulb is:

1. 0.5 Ω
2. 6 Ω
3. 12 Ω
4. 24 Ω

Answer: 3. 12

Question 13. If 20 C of charge passes a point in a circuit in 1 s, what current is flowing?

Answer: Q = 20 C, t = Is; I = Q/t; Thus, I = 20/1 = 20 A

Question 14. What is an electric current?

Answer: An electric current is a flow of electric charges (electrons) through a conductor.

Question 15. Which effect of current is utilized in an electric light bulb?

Answer: The Heating effect of electric current.

Question 16. State the expression for electrical power in terms of potential difference and resistance.

Answer: Electrical power, P = V²/R

Question 17. Name a device that helps to measure the potential difference across a conductor.

Answer: Voltmeter

Question 18. If a charge of 420 C is flowing from the wire for 5 minutes. Find the value of current.

Answer: 1 = q/t; q = 420 C; t = 5 minutes = 5 x 60 = 300 s ; I = 420/300 = 1.4 A

Question 19. How does the resistance of a pure metal change if its temperature decreases?

Answer: On decreasing the temperature, the resistance decreases.

Question 20. How many milliamperes are there in 1 ampere?

Answer: 1A = 10²mA

Question 21. Why should the resistance of an ammeter be very small?

Answer: The resistance of an ammeter should be very small so that it may not change the value of the current flowing in the circuit.

Question 22. An electron enters a magnetic field at right angles to it, as shown in the figure. What is the direction of force acting on the electron?

Answer: The direction of force is perpendicular to the direction of magnetic field and current as given by Fleming’s left hand rule. We know that the direction of current is taken opposite to the direction of motion of electrons. The force is therefore directed into the page.

Chapter 3 Electricity Short Questions And Answers

Question 1. Why it necessary to connect an earth wire to electric appliances having metallic bodies?

Answer:

An electric appliance with having metallic body can have current leak and current may flow through its body. It can be fatal if a person touches its current-carrying metallic body. So, it must be connected to an earth wire to pass the extra current, flowing through its body, to the earth plate.

Question 2. Two resistors each of 10 Ω are connected in

1. Series
2. And then in parallel to a battery of 6 V. Calculate the ratio of power consumed in the combination of resistor in two case.

Answer:

V = 6V; Total resistance in series, Rs = 20 Ω

Power, P_s = V²/R = 1.8 W; Total resistance in parallel, R_p = 5 Ω; Power, P_p = V²/R = 7.2 W

P_s/P_p = 1.8/7.2 = 4

Question 3. An electrical appliance is rated 240 V, 500 W. How much current will this appliance draw? It is planned to spend Rs 200 for running this appliance in a month. If the per unit cost is Rs 4.60, how many hours can this appliance be operated in a month of 30 days?

Answer:

Let the running time per day be “n” hours.

Running cost for 30 days = n x 0.5 x 4.60 x 30 = 200

Hence, n = 200/ (0.5 x 4.60 x 30) = 2 hours 54 minutes.

Question 4. Observe the given table, in which the values of current flowing through a conductor for corresponding values of potential difference across the conductor.

1. Plot a graph between current and voltage.
2. Calculate the resistance of the conductor.

Answer:

Resistance, R = V/l = 10/0.4 = 25 Ω

Question 5. Draw a schematic labelled diagram of a closed circuit which connects all the given components in series and is connected across a 12 V battery:

1. 20 W lamp
2. An ammeter
3. A switch
4. 10 Ω/100 W resistor

Answer:

Question 6. The circuit diagram given below shows the combination of three resistors R1, R2 and R3:

Find:

1. Total resistance of the circuit.
2. Total current flowing in the circuit.

Answer:

The total resistance of two resistors that are connected in parallel is

1/R’ = 1/3+1/6 1/R’ = 3/6 R’ = 2 Ω

Total resistance of the circuit = 2+4 = 6 Ω

Total current flowing through the circuit = V/total resistance

I = 12/6 = 2 A

Question 7. Study the circuit and find:

1. Total resistance in arm CE
2. Current in arm AB

Answer:

Total resistance in arm CE Rs = 6 + 6 = 12 Ω

Current in arm AB, I = 5V/17 0 = 0.29A

Question 8. Observe the table given below and answer the questions:

1. What does the symbol (1) in the table given above represents?
2. Which electrical component is represented when symbol (2) is used in circuit diagram?

Answer:

1. Ammeter
2. Rheostat

Question 9. Draw a circuit diagram to show how 3 bulbs can be lit from a battery so that 2 bulbs are controlled by the same switch while the third bulb has its own switch.

Answer:

Question 10. An electric heater connected to the 240 V main supply draws a current of 10 A. Find:

1. Power of the heater
2. Energy consumed in 2 minutes

Answer:

P = VI P = 240 x 10 = 2400 W

Energy consumed = Vlt = 2400 x 120 = 28800 Joules

Question 11. When a 6Ω resistor is connected across the terminals of an 18 V battery, Calculate the coulomb passing through the resistor per second.

Answer:

V = IR; 18 =I x 6; I = 3A = 3C/s

Question 12. Name the black substance of pencil. Will the current flow through the electrical circuit when we use the sharpened ends of the pencil to complete the circuit?

Answer:

Graphite. Yes, current will flow through the circuit since graphite is a good conductor of electricity.

Question 13.

1. Which gas is filled in an electric bulb and why?
2. State Ohm’s law.

Answer:

1. Argon or neon gas is filled in electric bulbs. These gases are used because they are inactive or inert. This prolongs the life of the filament,
2. Ohm’s law: At a constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends.

Question 14. The values of potential difference V applied across a resistor and the corresponding values of current I flowing in the resistor are given below:

1. What is the nature of the V-l graph plotted for the above values of potential difference and current?
2. Which law is illustrated by such a type of graph?

Answer:

1. Straight line graph
2. Ohm’s law is illustrated when the nature of V-1 graph is a straight line.

Question 15. From the following electric circuit:

Calculate:

1. Resultant resistance and current
2. Heat energy evolved when the circuit is switched on for 30 minutes

Answer:

For the given circuit,

1. Resultant resistance, R_eq = 10.33 Ω; Total current, I = V/R_eq = 6/ 10.33 = 0.58 A
2. Heat energy evolved in this circuit if it is switched on for 30 min. By Joule’s law of heating, H = l²Rt = (0.58)² x 10.33 x 1800 = 6255J

Question 16.

1. Define power,
2. What is the SI unit of power?
3. What is the commercial unit of electrical energy?

Answer:

1. Work done per unit time is called power,
2. The SI unit of power is Watt (W).
3. The commercial unit of electrical energy is kilowatt-hour (kWh)

Question 17. Three resistors of 5Ω, 10Ω, and 20Ω, respectively, are connected to a battery of 12 V as shown in the circuit given below.

Calculate:

1. Current through each resistor
2. Total current in the circuit
3. Total resistance of the circuit

Answer:

Effective resistance for the parallel combination of 5 Ω and 20 Ω is given by 1/R = 20+5

20×5; R=4 . Hence, total resistance in the circuit 12 + 4 = 16 Ω.

Current drawn from the battery = 16/12 = 4/3 = 1.33 A

1. Potential difference across the parallel combination of resistors is (4/3) x 4 = (16/3) V. Hence, current through 5 Ω resistor is (16/15) A and current through 20 Ω resistor is (16/60) =(4/15) A.
2. Total current drawn from the battery (4/3) = 1.33 A
3. Total resistance in the circuit 12 + 4 = 16

Question 18. An electric appliance of 1.5 kW power rating operates on a 220V main supply and has a current rating of 5 A. Is this fuse suitable for this electrical appliance? Explain.

Answer:

Power, P = 1.5 kW = 1500 W; V = 220 V; Current drawn, P = V x I

Therefore, I = P/V = 1500/220 = 6.81 A ≈ 7 A

The current drawn by the electrical appliance is 7 A, which is beyond the fuse rating capacity in the circuit, therefore, it will melt and break the circuit.

Hence, the fuse wire of 5 A rating would not be suitable for this electrical appliance.

Question 19.

1. Write the expression for the relationship between resistance and resistivity.
2. A 1.25 kW electric oven is connected to a 230 V power source. Calculate
   • Electric current passing through the oven
   • Resistance of the oven
   • Electric energy consumed in a 4-hour use of the oven

Answer:

1. ρ = R x A/ I, where ρ = resistivity of material, R = Resistance of conductor, I = Length of conductor
2. Power rating of the oven, P = 1.25 kW = 1250 W ; Potential difference of the power supply, V = 230 V
   • Power, P = V x I; Therefore, I = P/V = 1250/230 = 5.43 A
   • Resistance and power are related as P = V²/R; Therefore, R = V²/P = (230)²/1250 = 42.32 Ω
   • Energy consumed by the oven is E = P x t = 1.25 kW x 4 h = 5 kWh

Question 20. If three resistors of 6 Ω, 7 Ω, and 10 Ω are connected in series. Calculate the equivalent resistance in the circuit.

1. What is the potential difference across the three resistors R1, R2, and R3 in a series combination if the potential across the circuit is V?
2. What is the current along each of the resistors in a series combination if the current flowing in the circuit is I?
3. Is the equivalent resistance in the parallel combination of resistors more than the value of each individual resistor?

Answer:

Equivalent resistance when the resistors are connected in series is R_s = R₁ + R₂ + R₃

Therefore, R_s = 6 + 7 + 10 = 23 ohm

The potential difference (PD) across each resistor will be different in a series combination.

Across resistor R₁, PD will be V₁; for R₂, PD will be V_2, and for R₃, PD will be V₃.

The current across the three resistors in a series combination will be the same, i.e., T.

No, when the resistors are connected in parallel, the equivalent resistance is less than each of the individual resistors.

Question 21. An electric heater of resistance 10 Ω and a resistance wire of 8 Ω are connected in series with a 6 V battery. Find:

1. Current through the circuit
2. Potential difference across the electric heater
3. Potential difference across an electric wire.

Answer:

1. V = IR

6 = I x (8+10)

I = 6/18 = 1/3A

2. V_{electric heater}= 1/3 x 10 = 10/3 V

3. V_{electric wire}=1/3×8 = 8/3 V

Question 22. In the given circuit, calculate

Total resistance of the circuit

Current flowing through the circuit

Potential difference across the lamp and the resistor

1. Total resistance R = R₁ + R₂ = 18 Ω + 6Ω = 24 Ω;
2. Current flowing through the circuit, I = V/R = 6/24 = 0.25 A;
3. Potential difference across the lamp, V₂ = IR₁ = 0.25 x 18 = 4; Potential difference across the resistor R₂, V₂ = IR₂ = 0.25 x 6 = 1.5 V

Question 23. An electrical appliance is rated 200 V, 100 W. What is the resistance of the appliance? Five such appliances run simultaneously for 4 hours. What is the energy consumed? Calculate the cost of running these appliances if the per unit cost is Rs 4.60.

Answer:

Rating of the electrical appliance is 200 V-100 W. Since P = V²/R.

Therefore, R = V²/P = (200)²/100 = 400 Ω.

Total power consumed by 5 bulbs will be 500 W.

Hence, for a four-hour operation, the energy consumed is E = P x t

E = 500×4 = 2000 Wh = 2kWh

Cost of electricity per unit is Rs 4.60. Hence, the total cost is Cost = 2 x 4.60 = Rs 9.2

Question 24.

1. What is the function of an earth wire in electrical instruments? Why is it necessary to earth the metallic electric appliances?
2. Explain what is short-circuiting and overloading in an electric supply.

Answer:

1. The main function of earth wire is to absorb excess electricity passing through the appliance and to prevent overloading of live wire. The metallic appliances are earthed because whenever there is leakage of current, the leaked current passes thro ugh the earth wire to earth.
2. Short Circuit: When live wire comes in contact with Neutral wire then the resistance becomes zero and with Ohm’s law current becomes infinite. Overloading connected sWhen a large number of home appliances are simultaneously to the same socket and they withdraw large amounts of current than mentioned on the switch.

Chapter 3 Electricity Long Questions And Answers

Question 1.

1. The domestic electric supply of a house is through a 15 A fuse. Along with a 2000 W heater, how many 100 W bulbs can be used simultaneously in the house without causing overload? The domestic supply is 220 V all appliances are rated for 220 V.
2. What is meant by one cycle of alternating current? and
3. In a typical lightning strike, 2.5 C flows from the cloud to the ground in 0.20 milliseconds. What is the current during the strike?

Answer:

The current through the heater can be calculated as

I = P/V = 2000/ 220 = 100/11

Now the current rating through one bulb can be calculated in a similar way

i = P/V = 100/220 = 5/11

Now if there are n bulbs, then for the fuse the total current should be

15 = I + ni

15 = 100/11 + n x 5/11

15 x 11 -100 = 5n

n = 165-100/5 =13

Therefore, a total of 13 bulbs can be used simultaneously.

Question 2.

1. Derive an expression for the heat produced in a conductor of resistance R when a current I flows through it for time t.
2. Two identical resistors of resistance R are connected in series with a battery of potential difference V for time t. The resistors are then connected in parallel with the same battery for the same time t. Compare the heat produced in the two cases.

Answer:

A conductor offers resistance to the flow of current. Hence, work must be continuously done by the current to keep itself flowing.

When an electric charge Q moves against a potential difference V, the work done is

W = QV ….(1)

From the definition of current, Q = I x t ….(2)

From Ohm’s law, V = I x R …(3)

Therefore, W = I x t x I x R

Assuming that all this work goes in producing heat energy (H).

Therefore, the heat produced (H) in a conductor of resistance ‘R’ when current T is flowing for time ‘t’ is

H = I²Rt

2. When resistors are connected in series:

R_s + R + R = 2R

Therefore, H_s = V²/R_s = V²/2R …(1)

When resistors are connected in parallel:

∴ \(\frac{1}{R p}=\frac{1}{R}+\frac{1}{R}=\frac{2}{R}\)

Therefore, R_p = R/2

H_s = V²/ R_s = 2V²/R ….(2)

From (1) and (2)

∴ \(\frac{\mathrm{Hs}}{\mathrm{Hp}}=\frac{1}{4}\)

Therefore, H_p = 4H_s

Question 3. Derive the expression for equivalent resistance if three resistors R1, R2 and R3 are connected in a parallel combination.

Answer:

Derivation for equivalent resistance if three resistors are connected in parallel:

Potential difference in a parallel circuit remains the same across all resistors.

Current is the sum of the currents across all the individual resistors.

I = l₁ + I₂ + I₃ ….(1)

Let R_p be the resultant resistance of the circuit. On applying Ohm’s law to the entire circuit,

l = V/R_p ….(2)

Now applying Ohm’s law to individual resistances,

⇒ \(\left.\begin{array}{l}
\mathrm{I}_1=\mathrm{V} / \mathrm{R}_1 \\
\mathrm{I}_2=\mathrm{V} / \mathrm{R}_2 \\
\mathrm{I}_3=\mathrm{V} / \mathrm{R}_3
\end{array}\right]…..(3)\)

From equations (1), (2) and (3),

V/ R_p = V/R₁ + V/R₂ +V/R₃

Cancelling “V” on both sides, we get

1/ R_p =1/R₁ + 1/R₂ + 1/R₃

Question 4. A circuit has a fuse of 5 A. What is the maximum number of 110 W (220 V) bulbs that can be safely used in the circuit?

Answer:

Suppose ‘n’ bulbs can be used safely.

Power of ‘n’ bulbs, P = 110 x n Watt

Potential difference, V = 220 V; Current, I = 5 A

Power, P = V x I

110 xn =220 x 5/110

Thus, the maximum number of bulbs that can be connected safely in the circuit is 10.

Question 5.

1. List the factors on which the resistance of a conductor depends.
2. A 4-kW heater is connected to a 220-V power source. Calculate
   • Electric current passing through the heater
   • Resistance of the heater
   • Electric energy consumed in a 2-hour use of the heater

Answer:

1. Power, P = VI
   Therefore, I = P/V = 4000/220 = 18.18 A
2. P = V²/R
   Therefore, R = V²/P = (220)²/4000 = 12.1 Ω
3. E = P x t = 4 kW x 2 h = 8kWh

Question 6. What is meant by the statement ‘the potential difference between two points is 1 V? Study the circuit shown in which three identical bulbs B1, B2, and B3 are connected in parallel with a battery of 4.5 V.

1. What will happen to the glow of the other two bulbs if bulb B3 gets fused?
2. If the wattage of each bulb is 1.5 W, what readings will the ammeter A show when all the three bulbs glow simultaneously?
3. Find the total resistance of the circuit.

Answer:

Potential difference of 1 volt means that one joule of work is done to move a charge of one coulomb from one point to another.

1. If bulb B3 gets fused, then the other two bulbs will continue glowing with the same brightness.
2. When the bulbs are in parallel, wattage will be added (4.5 W) and the ammeter reading would be 45/45 = 1.0 ampere.
3. Since the ammeter reading is 1.0 ampere, the resistance of the combination = 4.5V/1.0A = 4.5 Ω

Question 7. In the given circuit, A, B, C and D are four lamps connected with a battery of 60V. Analyse the circuit to answer the following questions.

1. What kind of combination are the lamps arranged in (series or parallel)?
2. Explain with reference to your above answer, what are the advantages (any two) of this combination of lamps?
3. Explain with proper calculations which lamp glows the brightest?
4. Find out the total resistance of the circuit.

Answer:

1. The lamps are connected in parallel.

2. Advantages of parallel combination: If one lamp stops working, it will not affect the working of the other lamps. – Potential difference across each lamp will be same.

3. The lamp with the highest power will glow the brightest.

P=VI

Even if the potential difference across all the lamps are same, lamp C has the highest current.

Hence, for Lamp C, P=5 x 60 Watt = 300 W.

Thus, lamp C glows the brightest.

4. Total current, I = 3+4+5+3 A = 15A

Voltage = 60 V

Since V = IR,

Hence R = V/I = 60/15 A = 4 A.

Haryana Board Class 10 Physics Solutions For Sample Question Paper

Question 1. The change in colour of the moist litmus paper in the given set-up is due to 

• Presence of acid
• Presence of base
• Presence of H⁺(aq) in the solution
• Presence of Litmus which acts as an indicator

1. 1 and 2
2. Only 2
3. Only 3
4. Only 4.

Answer: 3. Only 3

Question 2. In the redox reaction

MnO₂ + 4HCI → MnCI₂ + 2H₂O + Cl₂

1. MnO₂ is reduced to MnCI₂ & HCI is oxidized to H₂O
2. MnO₂ is reduced to MnCI₂ & HCI is oxidized to Cl₂
3. MnO₂ is oxidized to MnCI₂ & HCI is reduced to Cl₂
4. MnO₂ is oxidized to MnCI₂ & HCI is reduced to H₂O

Answer: 2. MnO₂ is reduced to MnCI₂ & HCI is oxidized to Cl₂

Question 3. Which of the following is the correct observation of the reaction shown in the setup?

1. Brown powder of Magnesium oxide is formed.
2. Colourless gas, which turns lime water milky, is evolved.
3. Magnesium ribbon burns with brilliant white light.
4. Reddish brown gas with a smell of burning Sulphur has evolved.

Answer: 3. Magnesium ribbon burns with brilliant white light.

Question 4. With reference to the four gases CO₂, CO, Cl₂ and O₂, which one of the options in the table is correct?

Answer: 2.

Question 5. On placing a copper coin in a test tube containing green ferrous sulphate solution, it will be observed that the ferrous sulphate solution

1. Turns blue, and a grey substance is deposited on the copper coin.
2. Turns colourless, and a grey substance is deposited on the copper coin.
3. Turns colourless, and a reddish-brown substance is deposited on the copper coin.
4. Remains green with no change in the copper coin.

Answer: 4. Remains green with no change in the copper coin.

Question 6. Anita added a drop each of diluted acetic acid and diluted hydrochloric acid on pH paper and compared the colours. Which of the following is the correct conclusion?

1. pH of acetic acid is more than that of hydrochloric acid.
2. pH of acetic acid is less than that of hydrochloric acid.
3. Acetic acid dissociates completely in aqueous solution.
4. Acetic acid is a strong acid

Answer: 1. pH of acetic acid is more than that of hydrochloric acid.

Question 7. The formulae of four organic compounds are shown below. Choose the correct option

1. A and B are unsaturated hydrocarbons
2. C and D are saturated hydrocarbons
3. Addition of hydrogen in the presence of a catalyst changes A to C
4. The addition of potassium permanganate changes B to D

Answer: 3. Addition of hydrogen in the presence of a catalyst changes A to C

Question 8. In the given transverse section of the leaf, identify the layer of cells where maximum photosynthesis occurs.

1. 1, 2
2. 2, 3
3. 3, 4
4. 1, 4

Answer: 2. 2, 3

Question 9. Observe the experimental setup shown below. Name the chemical indicated as ‘X’ that can absorb the gas which is evolved as a byproduct of respiration.

1. NaOH
2. KOH
3. Ca (OH)₂
4. K₂C0₃

Answer: 2. KOH

Question 10. If a tall pea plant is crossed with a pure dwarf pea plant, then what percentage of F1 and F2 generations, respectively, will be tall?

1. 25%, 25%
2. 50%, 50%
3. 75%,100%
4. 100%, 75%

Answer: 4. 100%, 75%

Question 11. Observe the three figures given below. Which of the following depicts tropic movements appropriately?

1. B and C
2. A and C
3. B only
4. C only

Answer: 4. C only

Question 12. The diagram shown below depicts pollination. Choose the options that will show a maximum variation in the offspring.

1. A, B and C
2. B and D
3. B, C and D
4. A and C

Answer: 2. B, C and D

Question 13. A complete circuit is left on for several minutes, causing the connecting copper wire to become hot. As the temperature of the wire increases, the electrical resistance of the wire

1. Decreases
2. Remains the same
3. Increases
4. Increases for some time and then decreases.

Answer: 3. Increases

Question 14. A copper wire is held between the poles of a magnet.

The current in the wire can be reversed. The pole of the magnet can also be changed over. In how many of the four directions shown can the force act on the wire?

1. 1
2. 2
3. 3
4. 4

Answer: 2. 2

Question 15. Plastic insulation surrounds a wire having a diameter d and a length I as shown above. A decrease in the resistance of the wire would be produced by an increase in the

1. Length I of the wire
2. Diameter d of the wire
3. Temperature of the wire
4. Thickness of the plastic insulation

Answer: 2. Diameter d of the wire

Question 16. Which of the following patterns correctly describes the magnetic field around a long straight wire carrying current?

1. Straight lines perpendicular to the wire,
2. Straight lines parallel to the wire,
3. Radial lines originating from the wire,
4. Concentric circles centred around the wire.

Answer: 4. Concentric circles centred around the wire.

Assertion – Reasoning Based Questions And Answers

These consist of two statements: Assertion (A) and Reason (R). Answer these questions by  selecting the appropriate option given below:

1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, and R is not the correct explanation of A
3. A is true, but R is false
4. A is False, but R is true

Question 1. Assertion: Silver bromide decomposition is used in black and white photography.

Reason: Light provides energy for this exothermic reaction.

Answer: 3. A is true but R is false

Question 2. Assertion: Height in pea plants is controlled by efficiency of enzymes and is thus genetically controlled.

Reason: Cellular DNA is the information source for making proteins in the cell.

Answer: 1. Both A and R are true, and R is the correct explanation of A.

Question 3. Assertion: Amphibians can tolerate mixing of oxygenated and deoxygenated blood.

Reason: Amphibians are animals with a chambered heart.

Answer: 3. A is true but R is false.

Question 4. Assertion: On freely suspending a current-carrying solenoid, it comes to rest in the Geographical N-S direction.

Reason: One end of the current-carrying straight solenoid behaves as a North pole and the other end as a South pole, just like a bar magnet.

Answer: 1. Both A and R are true, and R is the correct explanation of A.

Very Short Answer Questions And Answers

Question 1. A clear solution of slaked lime is made by dissolving Ca(OH)₂ in an excess of water. This solution is left exposed to the air. The solution slowly goes milky as a faint white precipitate forms. Explain why a faint white precipitate forms, and support your response with the help of a chemical equation.
OR
Keerti added dilute Hydrochloric acid to four metals and recorded her observations as shown in the table given below:

Select the correct observation(s) and give chemical equation(s) of the reaction involved.

Answer:

Calcium hydroxide reacts with Carbon dioxide present in the atmosphere to form Calcium carbonate which results in milkiness or white ppt or Formation of Calcium carbonate \(\mathrm{Ca}(\mathrm{OH})_2+\mathrm{CO}_2 \rightarrow \mathrm{CaCO}_3+\mathrm{H}_2 \mathrm{O}\)

or

⇒ \(\mathrm{Fe}+\mathrm{HCl} \rightarrow \mathrm{FeCl}_2 / \mathrm{FeCl}_3+\mathrm{H}_2\) (No deduction for balancing/ states)

∴ \(\mathrm{Zn}+\mathrm{HCl} \rightarrow \mathrm{ZnCl}_2+\mathrm{H}_2\)

Question 2. How is the mode of action in the beating of the heart different from reflex actions? Give four examples.

Answer:

Question 3. Patients whose gallbladders are removed are recommended to eat less oily food. Why?

Answer:

The gallbladder stores bile, which helps in the emulsification of lipids.

In the absence of stored bile, emulsification of fats will be negligible or affected or less and thus fat digestion will be slow. Hence, there are such diet restrictions.

Question 4. Name the substances, other than water, that are reabsorbed during urine formation. What are the two parameters that decide the amount of water that is reabsorbed in the kidney?

Answer:

Glucose, amino acids, salts and a major amount of water are selectively reabsorbed as the urine flows along the tube.

The amount of water reabsorbed depends on how much excess water there is in the body and on how much dissolved waste there is to be excreted.

Question 5. State the phenomena observed in the diagram. Explain with reference to the diagram, which of the two lights mentioned above will have the higher wavelength?

How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.

Answer:

Dispersion- The splitting of white light into seven colours on passing through a prism.

Velocity is directly proportional to wavelength, given a constant frequency. So yellow will have a greater wavelength than blue as the velocity of yellow light is greater than blue.
or
The angles of deflection of the two prisms need to be equal and opposite. While the first prism splits the light in the seven colours due to different angles of deflection, the second prism combines the spectrum along a single ray and the colours again combine to give white light as the emergent light.

Question 6. A lot of waste is generated in the neighborhood. However, almost all of it is biodegradable. What impact will it have on the environment or human health?

Answer:

Excess generation of biodegradable wastes can be harmful as – Its decomposition is a slow process leading to production of foul smell and gases.

It can be the breeding ground for germs that create unhygienic conditions.

Short Answer Questions And Answers

Question 1.

Identify the types of reaction mentioned above in (1) and (2). Give one example for each type in the form of a balanced chemical equation.

Answer:

1. Displacement
   • \(\mathrm{Fe}(\mathrm{~s})+\mathrm{CuSO}_4(\mathrm{aq}) \rightarrow \mathrm{FeSO}_4(\mathrm{aq})+\mathrm{Cu}(\mathrm{~s})\)
   • \(\mathrm{Zn}(\mathrm{~s})+\mathrm{CuSO}_4(\mathrm{aq}) \rightarrow \mathrm{ZnSO}_4(\mathrm{aq})+\mathrm{Cu}(\mathrm{~s})\)
   • \(\mathrm{Pb}(\mathrm{~s})+\mathrm{CuCl}_2(\mathrm{aq}) \rightarrow \mathrm{PbCl}_2(\mathrm{aq})+\mathrm{Cu}(\mathrm{~s})\)
2. Double displacement
   • \(\mathrm{Na}_2 \mathrm{SO}_4(\mathrm{aq})+\mathrm{BaCl}_2(\mathrm{aq}) \rightarrow \mathrm{BaSO}_4(\mathrm{~s})+2 \mathrm{NaCl}(\mathrm{aq})\)

Question 2.

1. Identify the gases evolved at the anode and cathode in the above experimental set-up.
2. Name the process that occurs. Why is it called so?
3. Illustrate the reaction of the process with the help of a chemical equation.

Answer:

1. Anode: Chlorine; Cathode: Hydrogen
2. Chlor alkali process as the products obtained are alkali, chlorine gas and hydrogen gas Electric current
3. \(2 \mathrm{NaCl}(\mathrm{aq})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{I}) \longrightarrow 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{Cl}_2(\mathrm{~g})+\mathrm{H}_2(\mathrm{~g})\)

Question 3. The leaves of a plant were covered with aluminium foil, how would it affect the physiology of the plant?
OR
How is lymph an important fluid involved in transportation? If lymphatic vessels get blocked, how would it affect the human body? Elaborate.

Answer:

No photosynthesis will occur, so no glucose will be made. Also, no respiration will take place as no Oxygen will be taken in.

No transpiration will occur, so there will be no upward movement of water or minerals from the soil as there will be no transpirational pull.

Temperature regulation of the leaf surface will be affected.
or
Lymph carries digested and absorbed fat from the intestine and drains excess fluid from the extracellular space back into the blood.

Blockage of the lymphatic system will lead to water retention and poor fat absorption in the body.

Question 4. Rohit wants to have an erect image of an object using a converging mirror of focal length 40 cm.

1. Specify the range of distances where the object can be placed in front of the mirror. Justify.
2. Draw a ray diagram to show image formation in this case.
3. State one use of the mirror based on the above kind of image formation.

Answer:

1. The object has to be placed at a distance between 0 – 40 cm. This is because the image is virtual, erect and magnified when the object is placed between F and P.

3. Used as a shaving mirror or used by dentists to get an enlarged image of teeth

Question 5.

1. A lens of focal length 5 cm is being used by Debashree in the laboratory as a magnifying glass. Her least distance of distinct vision is 25 cm.
   • What is the magnification obtained by using the glass?
   • She keeps a book at a distance 10 cm from her eyes and tries to read. She is unable to read. What is the reason for this?
2. Ravi kept a book at a distance of 10 cm from the eyes of his friend Hari. Hari is not able to read anything written in the book. Give reasons for this?

Answer:

1. Image distance, v = -25 cm

Focal length, f = 5 cm

Magnification, m =?

From the lens formula

⇒ \(\frac{1}{\mathrm{f}}=\frac{1}{v}-\frac{1}{u}\)

Therefore,

⇒ \(\frac{1}{u}=\frac{1}{-25}-\frac{1}{5}=-\frac{6}{25}\)

Object distance, \(u=-\frac{25}{6}\)

Since \(m=\frac{v}{u}=-\frac{25 x 6}{-25}=6 \mathrm{~cm}\)

2. This is because the least distance of distinct vision is 25 cm.

Question 6. A student fixes a white sheet of paper on a drawing board. He places a bar magnet in the centre and sprinkles some iron filings uniformly around the bar magnet. Then he taps gently and observes that iron filings arrange themselves in a certain pattern.

1. Why do iron filings arrange themselves in a particular pattern?
2. Which physical quantity is indicated by the pattern of field lines around the bar magnet?
3. State any two properties of magnetic field lines.

OR

A compass needle is placed near a current-carrying wire. State your observations for the following cases and give reasons for the same in each case:

1. The magnitude of the electric current in the wire is increased.
2. The compass needle is displaced away from the wire.

Answer:

1. When iron filings are placed in a magnetic field around a bar magnet, they behave like tiny magnets. The magnetic force experienced by these tiny magnets makes them rotate and align themselves along the direction of the field lines.
2. The physical property indicated by this arrangement is the magnetic field produced by the bar magnet.
3. Magnetic field lines never intersect; magnetic field lines are closed curves.

OR

1. The deflection in the compass needle increases as the Magnetic field of the current-carrying conductor is directly proportional to the current flowing through it.
2. The deflection in the needle decreases as the magnetic field is inversely proportional to the perpendicular distance from the wire.

Question 7. Why is damage to the ozone layer a cause for concern? What are its causes, and what steps are being taken to limit this damage?

Answer:

Damage to the ozone layer is a cause for concern because the ozone layer shields the surface of Earth from harmful UV radiations from the sun, which cause skin cancer in human beings.

Synthetic chemicals like chlorofluorocarbons (CFCs), which are used as refrigerants and in the fire

• Extinguishers are the main reason for the depletion of the ozone layer.
• Steps taken to limit this damage – Many developing and developed countries have signed and are obeying the directions of UNEP (United Nations Environment Programme) to freeze or limit the production and usage of CFCs at 1986 levels.

Long Answer Questions And Answers

Question 1. Shristi heated Ethanol with a compound A in presence of a few drops of concentrated sulphuric acid and observed a sweet smelling compound B is formed. When B is treated with sodium hydroxide it gives back Ethanol and a compound C.

1. Identify A and C
2. Give one use each of compounds A and B.
3. Write the chemical reactions involved and name the reactions.

OR

1. What is the role of concentrated Sulphuric acid when it is heated with Ethanol at 443 K. Give the reaction involved.
2. Reshu by mistake, forgot to label the two test tubes containing Ethanol and Ethanoic acid.
3. Suggest an experiment to identify the substances correctly? Illustrate the reactions with the help of chemical equations.

Answer:

1. A – Ethanoic acid Or any other carboxylic acid , C- Sodium salt of ethanoic acid or any other carboxylic acid or sodium ethanoate

2. Use of A- dil solution used as vinegar in cooking or preservative in pickles
Use of B-making perfumes, flavoring agent

3. \(\mathrm{CH}_3 \mathrm{COOH}+\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} \longrightarrow \mathrm{CH}_3 \mathrm{COOC}_2 \mathrm{H}_5+\mathrm{H}_2 \mathrm{O}\)

⇒ \(\mathrm{CH}_3 \mathrm{COOC}_2 \mathrm{H}_5+\mathrm{NaOH} \longrightarrow \mathrm{CH}_3 \mathrm{COONa}+\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}\)

Or

1. Sulphuric acid acts as a dehydrating agent

2. By reaction with sodium carbonate or bicarbonate 1M with the samples, ethanol will not react whereas ethanoic acid gives brisk effervescence.

⇒ \(2 \mathrm{CH}_3 \mathrm{COOH}+\mathrm{Na}_2 \mathrm{CO}_3 \longrightarrow \mathrm{CH}_3 \mathrm{COONa}+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2\)

or

∴ \(\mathrm{CH}_3 \mathrm{COOH}+\mathrm{NaHCO}_3 \longrightarrow \mathrm{CH}_3 \mathrm{COONa}+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2\)

Question 2.

1. Why is it not possible to reconstruct the whole organism from a fragment in complex multicellular organisms?
2. Sexual maturation of reproductive tissues and organs is are necessary link for reproduction. Elucidate.

OR

1. How are variations useful for species if there is a drastic alteration in the niches?
2. Explain how the uterus and placenta provide necessary conditions for the proper growth and development of the embryo after implantation.

Answer:

1. The reason is that many multi-cellular organisms are not simply a random collection of cells. Specialised cells are organised as tissues, and tissues are organised into organs, which then have to be placed at definite positions in the body. Therefore, cell-by-cell division would be impractical.
2. Sexual maturation of reproductive tissues is a necessary link for reproduction because of the need for specialised cell called germ-cells to participate in sexual reproduction. The body of the individual organism has to grow to its adult size, the rate of general body growth begins to slow down, reproductive tissues begin to mature.

A whole new set of changes in the appearance of the body takes place like change in body proportions, new features appear. This period during adolescence is called puberty. There are also changes taking place that are different between boys and girls. In girls, breast size begins to increase, with darkening of the skin of the nipples at the tips of the breasts. Also, girls begin to menstruate at around this time. Boys begin to have new thick hair growth on the face and their voices begin to crack.

or

1. If the niche were drastically altered, the population could be wiped out. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Variation is thus useful for the survival of species over time..
2. The lining of the uterus thickens and is richly supplied with blood to nourish the growing embryo.
   • The embryo gets nutrition from the mother’s blood with the help of placenta. It is embedded in the uterine wall.
   • It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi.
   • This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The developing embryo will also generate waste substances which can be removed by
     transferring them into the mother’s blood through the placenta.
   • The child is born as a result of rhythmic contractions of the muscles in the uterus.

Question 3.

The diagram above is a schematic diagram of a household circuit. The house shown in the above diagram has 5 usable spaces where electrical connections are made. For this house, the mains have a voltage of 220 V and the net current coming from the mains is 22A.

1. What is the mode of connection to all the spaces in the house from the mains?
2. The spaces 5 and 4 have the same resistance and spaces 3 and 2 have respective resistances of 20Ω and 30Ω. Space 1 has a resistance double that of space 5. What is the net resistance for space 5.
3. What is the current in space 3?
4. What should be placed between the main connection and the rest of the house’s electrical appliances to save them from accidental high electric current?

Answer:

1. All spaces are connected in parallel.

2. Let Resistance of Space 5 and 4 be R ohms respectively

Resistance of Space 1 = 2 R ohms

Resistance of Space 2 = 30 ohms

Resistance of Space 3 = 20 ohms

Current = 22 A V= 220 V

Total Resistance= V/I

⇒ \(\frac{1}{R 1}+\frac{1}{R 2}+\frac{1}{R 3}+\frac{1}{R 4}+\frac{1}{R 5}+\frac{1}{R 6}=\frac{1}{R e q}\)

⇒ \(\frac{1}{2 R}+\frac{1}{30}+\frac{1}{20}+\frac{1}{R}+\frac{1}{R}=\frac{1}{R e q}\)

∴ \(\frac{150}{60 R}+\frac{5 R}{60 R}=\frac{1}{R e q}\)

R = 150.

Case-Based Or Data -Based Questions And Answers

Question 1. Two students decided to investigate the effect of water and air on the iron object under identical experimental conditions. They measured the mass of each object before placing it partially immersed in 10 ml of water. After a few days, the objects were removed, dried, and their masses were measured. The table shows their results.

1. What might be the reason for the varied observations of the two students?

2. In another setup up the students coated iron nails with zinc metal and noted that iron nails coated with zinc prevent rusting. They also observed that zinc initially acts as a physical barrier, but an extra advantage of using zinc is that it continues to prevent rusting even if the layer of zinc is damaged. Name this process of rust prevention and give any two other methods to prevent rusting.

or

2. In which of the following applications of Iron will rusting occur most? Support your answer with a valid reason.

A – Iron Bucket electroplated with Zinc B – Electricity cables having iron wires covered with aluminium C – Iron hinges on a gate D – Painted iron fence.

Answer:

1. Rusting occurs in both A and B, so there is an increase in mass.

As the surface area of B is greater, the extent of rusting is greater

2. Galvanisation

Oiling or greasing or painting or alloying or chromium plating or any other.

or

2. C – Iron hinges on a gate – Iron is in contact with both atmospheric oxygen and moisture or water vapour.

Question 2. Pooja has green eyes while her parents and brother have black eyes. Pooja’s husband Ravi has black eyes, while his mother has green eyes and his father has black eyes.

1. On the basis of the above given information, is the green eye colour a dominant or recessive trait? Justify your answer.

2. What is the possible genetic makeup of Pooja’s brother’s eye colour?

3. What is the probability that the offspring of Pooja and Ravi will have green eyes? Also, show the inheritance of eye colour in the offspring with the help of a suitable cross.

OR

4. 50% of the offspring of Pooja’s brother are green-eyed. With the help of cross show how this is possible.

Answer:

1. Yes, green eye colour is recessive as it will express only in a homozygous condition.

2. BB, Bb c. bb*Bb

∴ \(\begin{array}{|l|l|l|}
\hline & \mathrm{B} & \mathrm{~b} \\
\hline \mathrm{~b} & \mathrm{Bb} & \mathrm{bb} \\
\hline \mathrm{~b} & \mathrm{Bb} & \mathrm{bb} \\
\hline
\end{array}\)

Genetic cross – 50% of the offspring can have green eye colour

OR

3. Brother is heterozygous (Bb) and wife is green(bb)

Wife bb*Bb brother

∴ \(\begin{array}{|l|l|l|}
\hline & \mathrm{B} & \mathrm{~b} \\
\hline \mathrm{~b} & \mathrm{Bb} & \mathrm{bb} \\
\hline \mathrm{~b} & \mathrm{Bb} & \mathrm{bb} \\
\hline
\end{array}\)

50% of the offsprings can have green eye colour as per the cross shown.

Question 3.

The above images are of a specialized slide projector. Slides are small transparencies mounted in sturdy frames, ideally suited to magnification and projection, since they have a very high resolution and a high image quality. There is a tray where the slides are to be put into a particular orientation so that the viewers can see the enlarged erect images of the transparent slides. This means that the slides will have to be inserted upside down in the projector tray. To show her students the images of insects that she investigated in the lab, Mrs. Iyer brought a slide projector. Her slide projector produced a 500 times enlarged and inverted image of a slide on a screen 10 m away.

1. Based on the text and data given in the above paragraph, what kind of lens must the slide projector have?

2. If v is the symbol used for image distance and u for object distance, then with one reason state what will be the sign for v/u in the given case?

3. A slide projector has a convex lens with a focal length of 20 cm. The slide is placed upside down 21 cm from the lens. How far away should the screen be placed from the slide projector’s lens so that the slide is in focus?

OR

3. When a slide is placed 15 cm behind the lens in the projector, an image is formed 3 m in front of the lens. If the focal length of the lens is 14 cm, draw a ray diagram to show image formation. (not to scale)

Answer:

1. Convex Lens

2. Negative as the image is real and inverted.

3. l/f = 1/v-1/u 1/20

= 1/v-1/-20 1/v

= 1/20 – 1/21

= (21 – 20)/420

= 1/420

v = 420 cm

or

Haryana Board Class 10 Physics  Chapter 2 The Human Eye And The Colourful World Multiple Choice Questions And Answers

Question 1. In which part of the human eye the image of an object is formed?

1. Iris
2. Pupil
3. Retina
4. Cornea

Answer: 3. Retina

Question 2. A person gets out into the sunlight from a dark room. How does his pupil regulate and control the light entering the eye?

1. The size of the pupil will decrease, and less light will enter the eye
2. The size of the pupil will decrease, and more light will enter the eye
3. The size of the pupil will remain the same, but more light will enter the eye
4. The size of the pupil will remain the same, but less light will enter the eye

Answer: 1. The size of the pupil will decrease, and less light will enter the eye

Question 3. A person is seeing an object closer to his eyes. What changes in his eyes will take place?

1. The pupil size will expand
2. The ciliary muscles will contract
3. The focal length of the eye lens will increase
4. The light entering the eye will be more

Answer: 2. The ciliary muscles will contract

Question 4. A person standing at point Y is watching a car coming from point X to 0 as shown.

The table shows the variation in the parts of the eye while seeing the car at X and O

1. At X, the focal length is higher than that at O.
2. At O, the focal length is higher than that at X.
3. At X, the Ciliary muscle is thicker than at O.
4. At 0, the Ciliary muscle is thicker than at X.

Which change in the person’s eye would likely to occur while watching the car?

1. 1 and 3
2. 1 and 4
3. 2 and 3
4. 2 and 4

Answer: 2. 1 and 4

Question 5. A person went for a medical check-up and found that the curvature of his eye lens is increasing. Which defects is he likely to suffer from?

1. Myopia
2. Cataract
3. Presbyopia
4. Hypermetropia

Answer: 1. Myopia

Question 6. The image shows the ray diagram of a defective eye.

Which option shows the correction of the defect of the eye?

Answer: 4.

Question 7. Which image shows the deviation of light in a prism?

Answer:  

Question 8. The image shows a light ray incident on a glass prism.

The various angles are labelled in the image. Which angle shows the angle of incidence and angle of refraction, respectively?

1. A and D
2. B and E
3. C and F
4. D and F

Answer: 1. A and D

Question 9. The image shows the dispersion of the white light in the prism.

What will be the colours of the X, Y and Z?

1. X: red; Y: green; Z: violet
2. X: violet; Y: green; Z: red
3. X: green; Y: violet; Z: red
4. X: red; Y: violet; Z: green

Answer: 2. X: violet; Y: green; Z: red

Question 10. A ray of light is incident on one face of the prism, as shown.

How will the ray of light disperse in the prism?

Answer:

Question 11. Why do stars appear to twinkle at night?

1. Because the light of stars travels in a different medium
2. Because the distance of the star varies when Earth rotates
3. Because the star changes its position relative to Earth
4. Because the atmosphere reflects the light at different angles

Answer: 1. Because the light of stars travels in a different medium

Question 12. A student learns that the scattering of sunlight depends on the wavelength of the light and the size of particles present in the atmosphere. The student collects the data about the wavelength of the visible lights and the size of the particle, as shown.

Which particles will scatter blue light?

1. P and R
2. R and S
3. P and Q
4. Q and S

Answer: 3. P and Q

Question 13. A got his eye tested. The optician’s prescription for the spectacles was:

Left eye: -3 D

Right eye: -3.50 D

The person is having a defect of vision called:

1. Presbyopia
2. Myopia
3. Astigmatism
4. Hypermetropia

Answer: 3. Astigmatism

Question 14. A man finds it difficult to read the odometer on the dashboard of the car but is able to clearly read a distant road sign. Which of the following statements is correct about this man?

1. The near point of his eyes has receded away.
2. The near point of his eyes has come closer to him.
3. The far point of his eyes has receded away.
4. The far point of his eyes has come closer to him.

Answer: 1. The near point of his eyes has receded away.

Question 15. Figures a, b, c, respectively, indicate the point in case of:

1. The Hypermetropia eye, the myopic eye and the normal eye
2. The normal eye, the myopic eye and hypermetropic eye
3. The normal eye, the Hypermetropia eye and the myopic eye
4. The myopic eye, the normal eye and hypermetropic eye

Answer: 3. The normal eye, the Hypermetropia eye and the myopic eye

Question 16. In which of the following cases will no dispersion take place when sunlight passes through it?

Answer:

Chapter 2 The Human Eye And The Colourful World Very Short Questions And Answers

Question 1. By how much time the day would have been shorter if the Earth had no atmosphere?

Answer: 4 minutes

Question 2. What colour does the sky appear to an astronaut?

Answer: The Sky appears dark to astronauts.

Question 3. Which colour of light has the shorter wavelength- red or violet?

Answer: Violet

Question 4. Name the phenomenon due to which a swimming pool appears less deep than it really is.

Answer: Refraction of light

Question 5. Name the phenomenon due to which the stars seem higher in the sky than they actually are.

Answer: Atmospheric refraction of light.

Question 6. Why does the Sun appear white at noon?

Answer: The Sun is nearly overhead at noon. The sunlight has to pass through a much smaller portion of the Earth’s atmosphere. The scattering is much less, and thus, the Sun looks white.

Question 7. An object is moved closer to an eye. What changes must take place in the eye in order to keep the image in Sharp focus?

Answer: The shape of the eye-lens should must be changed by the ciliary muscles to make it thicker and increase its converging power in order to keep the image sharp and in focus.

Question 8. Name the part of our eyes that helps us to focus on near and distant objects in quick succession.

Answer: Ciliary muscles

Question 9. A person is advised to wear spectacles with concave lenses. What type of defect of vision is he suffering from?

Answer: Myopia or short-sightedness.

Question 10. A person can comfortably read a book but finds it difficult to read the number on a bus parked 5 m away from him. Name the type of defect of vision he is suffering from. Which type of lens should he use in his spectacles to correct his vision?

Answer: Myopia or short-sightedness. A concave lens should be used to correct his vision.

Question 11. Name the type of particles which act as a prism in the formation of the rainbow in the sky.

Answer: Water droplets present in the atmosphere.

Question 12. Give the condition required to achieve a larger magnification of a small object by a compound microscope?

Answer: To achieve a larger magnification of a small object, both the objective and the eyepiece of a compound microscope should have smaller focal lengths.

Chapter 2 The Human Eye And The Colourful World Short Questions And Answers

Question 1. A student observes the following phenomenon in the lab as a white light passes through a prism. Among many other colours, he observed the position of the two colours, Red and Violet.

What is the phenomenon called? What is the reason for the violet light to bend more than the red light?

Answer:

Dispersion. The speed of violet light inside the prism is the slowest, and that of red is the highest. Hence, the deviation of violet light is maximum and that of red is minimum.

Question 2.

1. Name the colour of light which undergoes
   • More scattering and
   • Less scattering while passing through the atmosphere.
2. Draw a ray diagram to show the formation of a rainbow.

Answer:

While passing through the atmosphere

1. Blue light undergoes more scattering, while
2. Red light undergoes less scattering.

Question 3. Observe the experimental setup given below and answer the following questions:

1. Out of blue light and red light, which one is scattered more easily?
2. What causes the scattering of the blue component of sunlight in the atmosphere?

Answer:

1. Blue light scatters more easily due to its smaller wavelength
2. Gas molecules are present in the air.

Question 4. Give reasons:

1. The extent of deviation of a ray of light on passing through a glass prism depends on its colour.
2. Lights of red colour are used for danger signals.

Answer:

1. The refractive index of a medium is different for different colours of light,
2. Due to a large wavelength, red colour is the least scattered and travels to longest distance.

Question 5. A student sitting at the back bench in a class is not able to see what is written on the blackboard. He, however, sees it clearly when sitting on the front seat at an approximate distance of 1.5 m from the blackboard. Draw ray diagrams to illustrate the image formation of the blackboard when he is seated at the

1. Back seat
2. Front seat.

Answer:

1. When a student is seated in the back seat

2. When a student is seated in the front seat

Question 6. How does the eye adjust itself to deal with light of varying intensity?

Answer:

The amount of light entering the eye is controlled by the pupil. If the intensity of the outside light is low, then the pupil expands to allow more light to enter the eye. If the outside intensity is high, then the pupil contracts so that less light enters the eye.

Question 7. How do we see colours?

Answer:

1. The retina of our eyes has a large number of light-sensitive cells. The cells on the retina are of two shapes:
2. Rod-shaped and cone-shaped. The rod-shaped cells of our retina respond to the intensity of light. The cone-shaped cells of our retina respond to colours. These cells make us see colours and distinguish between them. Thus cones make colour perception possible.

Question 8. When is a person said to have developed cataract in their eye? How is the vision of a person having cataracts restored?

Answer:

Cataract develops when the lens of a person becomes unclear due to the formation of a membrane over it. The vision of a person having cataract can be restored after getting cataract surgery done on the eye-lens having cataract. This defect cannot be corrected by any type of spectacle lenses.

Question 9. Why do we have two eyes? Binocular (or two-eyed) vision has several advantages, one of which is the ability to see the world in three dimensions.

Answer:

Binocular (or two-eyed) vision has several advantages, one of which is the ability to see the world in three dimensions.

Question 10.

1. Which property of light is rainbow formation based on?
2. Why is the rainbow not visible on polluted skies?

Answer:

1. Refraction, Dispersion and Total Internal Reflection of Light;
2. Pollution particles change how the air scatters and absorbs different colours of light.

Question 11. What material is the human lens made up of? How is that different from the artificial lenses which are installed in the eye during an eye surgery?

The human eye lens is made up of proteins. The main difference between an artificial eye and lens is that a human eye lens provides sight, whereas an artificial eye does not.

Answer:

The human eye lens is made up of proteins. The main difference between an artificial eye and lens is that a human eye lens provides sight, whereas an artificial eye does not.

Question 12. An old person is unable to see clearly nearby objects as well as distant objects. To correct the vision, what kind of lens will he require?

Answer:

The upper portion (concave lens) facilitates the distant vision, and the lower portion (convex lens) facilitates near vision. Hence, a bifocal lens should be used, whose upper portion is a concave lens and lower portion is a convex lens.

Question 13. Why are danger signal lights red in colour?

Answer:

Danger signal lights are red in colour because red colour is the least scattered by fog or smoke.

Question 14. How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.

Answer:

When an inverted prism is kept a little distance away from the prism causing dispersion or basically in the path of the split beam, the spectrum recombines to form white light.

Question 15. Which part of human eye helps in the perception of colours?

Answer:

The retina of the human eye has a large number of cone-shaped and rod-shaped cells. The rods respond to the intensity of light and the cones to the colours. These help us to perceive colours.

Question 16.

1. A person having a myopic eye used the concave lens of focal length 50cm. What is the power of the lens?
2. What property of the eye is the principle of motion, pictures

Answer:

1. The formula for the power of a lens is Power (P) = 1/f. P = 1/50 = 0.02 dioptre.
2. Refraction of light through the eye lens is the basic principle for the visualization of pictures and motion.

Question 17. What happens when ciliary muscles get relaxed and then get contracted?

Answer:

When ciliary muscles get relaxed then the lens becomes thin, due to which the focal length increases and we can easily see distant objects clearly. When we see the objects which are near to our eyes, then the ciliary muscles get contracted, due to which the curvature of the eye lens increases and the eye lens becomes thicker. Hence, focal length decreases, which enables us to see objects which are placed near our eyes.

Question 18. A child, while playing with his father, threw the spectacles of his father. Now, father is not able to read the newspaper. Identify the defect of vision and how it was corrected. Draw a ray diagram of the defect and also a correcting diagram of the defect.

Answer:

As the father of the child is not able to read the newspaper means he can’t see the nearby objects clearly. This means that the father is suffering from the defect of hypermetropia. In this defect, the near point becomes farther away from the normal near point. His spectacles were made up of a convex lens of proper focal length to correct his defect.

Question 19. Give reason:

1. Why do stars twinkle?
2. Why do the planets not twinkle?
3. Why does the sun appear reddish early in the morning?
4. Why does the sky appear dark instead of blue to an astronaut?
5. Why does the Sun appear white at noon?

Answer:

1. Stars appear to twinkle due to atmospheric refraction. The light of a star after the entry of light into Earth’s atmosphere undergoes refraction continuously (due to the different density of the layers of the atmosphere) till it reaches the surface of the Earth. As the path of light coming from stars keeps on changing, the apparent position of stars keeps changing, and the amount of light from stars entering the eye keeps twinkling. Due to this, a star sometimes appears bright and
   sometimes dim (called the twinkling effect),
2. The planets are much nearer to the Earth than stars, and because of this they can be considered as a large source of light. If a planet is considered to be a collection of a very large number of point sources of light, then the average value of change in the amount of light entering the eye from all point-sized light sources is zero. Due to this, the effect of twinkling is nullified.
3. The light coming from the sun passes through various denser layers of air in the Earth’s atmosphere before reaching our eyes near the horizon. Most of the part of blue light and light of small wavelengths gets scattered by dust particles near the horizon. So, the light reaching our eyes is of a large wavelength. Due to this, the sun appears reddish at the time of sunrise and sunset.
4. As an astronaut moves away from the atmosphere of Earth, the atmosphere becomes thin. Due to the absence of molecules (or dust particles) in the air, the scattering of light does not take place. Thus, the sky appears dark in the absence of scattering.
5. At noon, the Sun appears white because the light from the Sun is directly overhead and travels a relatively shorter distance. Thus, only blue and violet colours are scattered.

Question 20. On a rainy day, Ram reached his grandfather’s place in the village. On the way to the house, he saw a beautiful rainbow in the sky. In the night, he saw lots of twinkling stars in the clear sky. He was very excited to see this beautiful natural phenomenon, which he was not able to see in the city, where he lived with his father. Explain the phenomenon on the basis of science. Do you think that pollution in the atmosphere affects the formation of rainbows and the twinkling of stars? Do you agree with the fact that a pollution-free environment will strengthen such natural phenomena in the cities as well. Elaborate.

Answer:

The twinkling of stars is due to atmospheric refraction. The formation of a rainbow is due to dispersion, refraction and internal reflection. Yes, pollution in the atmosphere affects the formation of rainbows and the twinkling of stars, and a pollution-free environment will strengthen such natural phenomena in the cities as well.

Haryana Board Class 10 Physics Chapter 1 Light-Reflection And Refraction Multiple Choice Questions And Answers

Question 1. Which of the following mirrors is used by a dentist to examine a small cavity in a patient’s teeth?

1. Convex Mirror
2. Plane Mirror
3. Concave Mirror
4. Any Spherical Mirror

Answer: 3. Concave Mirror

Question 2. Which diagram shows image formation of an object on a screen by a converging lens?

Answer:

Question 3. Which of the following can make a parallel beam of light when light from a point source is incident on it?

1. Concave mirror as well as convex lens;
2. Convex mirror as well as concave lens.
3. Two plane mirrors placed at 90° to each-other;
4. Concave mirror as well as concave lens.

Answer: 1. Concave mirror as well as convex lens

Question 4. Consider these indices of refraction: glass: 1.52; air: 1.0003; water: 1.333. Based on the refractive indices of three materials, arrange the speed of light through them in decreasing order.

1. The speed of light in water > the speed of light in air > the speed of light in glass.
2. The speed of light in glass > the speed of light in water > the speed of light in air.
3. The speed of light in air > the speed of light in water > the speed of light in glass.
4. The speed of light in glass > the speed of light in air > the speed of light in water.

Answer: 3. The speed of light in air > the speed of light in water > the speed of light in glass.

Question 5. Examine the above figure and state which of the following options is correct? [One small box in the figure is equal to 1 cm]

1. The mirror has a focal length of -6 cm and will produce an image of magnification +1.
2. The mirror has a focal length of -3 cm and will produce an image of magnification -1.
3. The mirror has a focal length of -3 cm and will produce an image of magnification +1.
4. The mirror has a focal length of -6 cm and will produce an image of magnification -1.

Answer: 2. The mirror has a focal length of -3 cm and will produce an image of magnification -1.

Question 6. The angle of incidence from air to glass at the point 0 on the hemispherical glass slab is:

1. 45°
2. 0°
3. 90°
4. 180°

Answer: 2. 0°

Question 7. If the power of a lens is – 4.0 D, then it means that the lens is a

1. Concave lens of focal length -50 m;
2. Convex lens of focal length +50 cm
3. Concave lens of focal length -25 cm ;
4. Convex lens of focal length -25 m

Answer: 3. Concave lens of focal length -25 cm ;

Question 8. Rays from Sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object?

1. 30 cm in front of the mirror;
2. 15 cm in front of the mirror
3. Between 15 cm and 30 cm in front of the mirror;
4. More than 30 cm in front of the mirror

Answer: 1. 30 cm in front of the mirror

Question 9. If the real image of a candle flame formed by a lens is three times the size of the flame and the distance between lens and image is 80 cm, at what distance should the candle be placed from the lens?

1. -80cm
2. -40 cm
3. -40/3 cm
4. -80/3 cm

Answer: 4. -80/3 cm

Question 10. While looking at the above diagram, Navin concluded the following

• The image of the object will be a virtual one.
• The reflected ray will travel along the same path as the incident ray but in opposite direction.
• The image of the object will be inverted.
• This is a concave mirror and hence the focal length will be negative. Which one of the above statements are correct?

1. 1 and 2;
2. 1 and 3;
3. 2, 3 and 4;
4. 1, 2, 3 and 4

Answer: 3. 2, 3 and 4;

Question 11. In the diagram light is travelling through different media. It is noted by a scientist that ∠1= ∠3= ∠4 but ∠2 <∠l. Which of the following statement would be correct?

1. Medium 1 is the denser than medium 3 but it’s density is equal to medium 2.
2. Medium 2 is the rarest medium.
3. Medium 3 is denser than medium 1.
4. Medium 1 and 3 are essentially the same medium, but medium 2 is denser than 1 and 3.

Answer: 4. Medium 1 and 3 are essentially the same medium, but medium 2 is denser than 1 and 3.

Question 12. The refractive index of flint glass is 1.65 and that for alcohol is 1.36 with respect to air. What is the refractive index of the flint glass with respect to alcohol?

1. 0.82
2. 1.21
3. 1.11
4. 1.01

Answer: 2. 1.21;

Question 13. The given lens has a focal length of 10 cm. The object of height 2 mm is placed at a distance of 5 cm from the pole. Find the height of the image.

1. 4 cm
2. 6.67 mm
3. 4 mm
4. 3.33 mm

Answer: 3. 4 mm

Question 14. A ray passing through the centre of curvature of a concave mirror is inclined at an angle a to its principal axis. The angle of reflection for this ray equals:

1. (∝/2)°
2. 0°
3. ∝°;
4. 90°

Answer: 2. 0°

Question 15. Consider the situation where:

• An object is 3 cm (height)
• Mirror is concave with 6 cm focal length.
• Object is placed at the centre of curvature.

Which of the following options are correct?

1. The mirror will produce an image of magnification +1.5.
2. The mirror will produce an image of magnification -1.
3. The mirror will produce an image of magnification +1.
4. The mirror will produce an image of magnification -1.5.

Answer: 2. The mirror will produce an image of magnification -1

Question 16. If a ray passes from air to glass in a spherical glass slab and passes through the centre of the slab without deviation, then the angle of incidence from air to glass at the point on the glass slab is.

1. 45°
2. 0°
3. 90°
4. 180°

Answer: 2. 0°

Question 17. Naman draws a ray diagram for an object in front of a concave mirror. She draws a ray starting from the top of the object and falling on the mirror perpendicularly. The ray after reflection will

1. Pass through focus.;
2. Pass through pole.
3. Pass through the centre of curvature.;
4. Pass through any point on the principal axis.

Answer: 3. Pass through the centre of curvature.

Question 18. If the refractive index of water with respect to air is 1.33 and of that of glass with respect to air is 1.5 then

1. Water is optically denser than glass,
2. Air is optically densest of all the three media.
3. Air’s optical density is between glass and air.
4. Glass is optically denser than water.

Answer: 4. Glass is optically denser than water.

Question 19. A convex lens has a focal length of 10 cm. The object of height 2 mm is placed at a distance of 5 cm from the pole. Find the height of the image.

1. 4 cm
2. 6.67 mm
3. 4 mm
4. 3.33 mm

Answer: 3. 4 mm

Question 20. Magnification produced by a rear view mirror fitted in vehicles

1. Is equal to one
2. Can be more than or less than one depending upon the position of the object in front of it
3. Is less than one
4. Is more than one

Answer: 3. Is less than one

Question 21. A student has to do the experiment on finding the focal length of a given convex lens by using a distant object. She can do her experiment if she is also provided with

1. A lamp and a screen
2. A scale and a screen
3. A lamp and a scale
4. None of these

Answer: 2. A scale and a screen

Question 22. When the two opposite surfaces of the slab are not parallel, the emergent angle e and incident angle are related as

1. e < i ;
2. e > i;
3. Does not depend on the refractive index of the medium;
4. Depends on the refractive index of the medium

Answer: 4. Depends on the refractive index of the medium

Chapter 1 Light – Reflection And Refraction Very Short Questions And Answers

Question 1. If the object is placed at a distance of 15 cm in front of the concave mirror of focal length of 10 cm, then what will be the nature of the image?

Answer: The object is placed at 15 cm; this means that the object is placed between the focus and the centre of curvature of the concave mirror. When the object is placed between the focus and the centre of curvature of a concave mirror, the image formed is real, inverted and magnified.

Question 2. How is the linear magnification produced by concave mirror?

1. Less than 1 or equal to 1
2. Zero or 1
3. More than or equal to 1
4. Less than 1, more than 1 or equal to 1

Answer: 4. Less than 1, more than 1 or equal to 1

Question 3. Define power of lens.

Answer:

The ability of a lens to converge or diverge the rays of light is called power of a lens. It is equal to the reciprocal of the focal length. P = l/f (in metre)

Question 4. Which type of reflection of light leads to the formation of images?

Answer: Regular reflection

Question 5. What kind of mirror can have a focal length of, -10 cm?

Answer: Concave mirror (since focal length is negative)

Question 6. Refractive indices of carbon disulphide and ethyl alcohol are 1.63 and 1.36 respectively. Which is optically denser?

Answer: Carbon disulphide is denser than the ethyl alcohol.

Question 7. If an object is at an infinity in front of a convex lens, where is the image formed?

Answer: At focus F

Question 8. What is the nature of the image formed by a convex lens if the magnification produced by the lens is +3?

Answer: Since the magnification has positive value, the image will be virtual and erect

Question 9. Why convex mirror is preferred as rear-view mirror in vehicles?

Answer: Convex mirror is preferred as rear-view mirror in vehicles because it gives virtual, erect image when object is beyond focus and gives wide field of view.

Question 10. Define principal focus for spherical mirrors.

Answer: It is the point on principal axis at which the incident rays parallel to principal axis, after reflection either meet or appear to meet.

Question 11. In torches, search lights and headlights of vehicles, the bulb is placed:

1. Between the pole and the focus of the reflector
2. Very near to the focus of the reflector
3. Between the focus and centre of curvature of reflector
4. At the centre of curvature

Answer: 2. Very near to the focus of the reflector

Explanation: The rays of light passing through the principal focus will go parallel to principal axis after reflection thus, forming a concentrated beam of light. Thus, in torches, headlights the bulb is placed very near to focus of the reflector.

Question 12. Light travels more quickly through water than through glass. What is optically denser among the medium mentioned in the statement?

Answer: Glass is optically denser than water.

Question 13. When does the light bend away from the normal during refraction?

Answer: When lights rays pass from optically denser to optically rarer medium.

Question 14. Which type of mirror could be used as a dentist’s mirror?

Answer: Concave mirror

Question 15. What is the full form of MRI?

Answer: Magnetic Resonance Imaging.

Question 16. A converging lens has a focal length of 20 cm. What is the power of the lens?

Answer: As the lens is converging, the focal length is positive. We know that Power = 1/ focal length (in m) = 1/0.2 m = + 5D

Question 17. For what position of an object, a concave mirror forms a real image equal in size to the object?

Answer: At the centre of curvature.

Question 18. A man stands 10 m away in front of a large plane mirror. How far must he walk before he is 5 m away from his image?

1. 2.5 m
2. 4.5 m
3. 7.5 m
4. 5 m

Answer: 3. 7.5 m;

Explanation: To be 5 m away from his image, the man must be standing 2.5 m away from the mirror. Thus, image distance + object distance = 2.5 m + 2.5 m = 5 m; Initially, he is 10 m away from the mirror. So, the man must walk a distance of 10 m- 2.5 m = 7.5 m.

Question 19. The incident ray makes an angle of 30° with a plane mirror. What is the total angle between the incident ray and the reflected ray?

1. 60°
2. 30°
3. 120°
4. 80°

Answer: 3. 120°

Explanation: ∠i = 90° – 30° = 60°; Since ∠i = ∠r, therefore ∠r = 60°; Angle between incident ray and reflected ray = ∠i + ∠r = 60° + 60° = 120°.

Chapter 1 Light-Reflection And Refraction Short Questions And Answers

Question 1. The image of an object placed at 40 cm in front of a lens is obtained on a screen at a distance of 100 cm from it. Find the focal length of the lens.

Answer:

f = 28.57 cm

Question 2. A concave mirror produces two times magnified real image of an object placed at 20 cm in front of it. What is the position of the image?

Answer:

v = —20 cm; the image is located at a distance of 20 cm in front of the mirror.

Question 3. An object is placed between infinity and the pole of a convex mirror. Draw a ray diagram and also state the position, the relative size and the nature of the image formed.

Answer:

When an object is placed between infinity and the pole of a convex mirror, the image formed is

1. Behind the mirror at the focus (F)
2. Virtual and erect
3. Highly diminished.

Question 4. An object 20 cm from a spherical mirror gives rise to a virtual image 15 cm behind the mirror. Determine the magnification of the image and the type of the mirror used.

Answer:

m = 0.75; The magnification sign is positive while the value 0.75 is less than 1. This indicates that the mirror is convex mirror.

Question 5. What is the nature of the image formed by a convex lens if the magnification produced by the lens is +3?

Answer:

The image will be virtual and erect, since the magnification has positive value.

Question 6.

What type of lens is shown in the diagram on the right? What will happen to the parallel rays of light? Show by completing the ray diagram.

Your eye contains a convex lens. Why is it unwise to look at the sun?

Answer:

The lens shown in convex. The parallel rays will converge to a point called focus (F).

It is unwise to look at the sun because the convex lens focuses a lot of sun rays into our eyes and this may damage them.

Question 7. The diagrams show the appearance of a fork when placed in front of and close to two mirrors A and B, turn by turn.

1. Which mirror is convex?
2. Which mirror is concave? Give reasons for your choice.

Answer:

1. Mirror B is convex since it forms a smaller image of fork,
2. Mirror A is concave since it forms a larger image of fork.

Question 8. Observe the diagram and answer the questions based on the studied concepts.

1. Complete the given ray diagram.
2. Calculate the position of the image formed.

Answer:

2. v = —6.67 cm; Thus, the image is formed at a distance of 6.67 cm between the centre of curvature and the focus.

Question 9. In which of the following media: glass, water and diamond

1. Light travels slowest,
2. Light travels fastest. Justify your answer

Answer:

Refractive index of glass: 1.52 to 1.9; Refractive index of water: 1.33; Refractive index of diamond: 2.42 – A substance having higher refractive index is optically denser then the substance of lower refractive index and light will travel slowest in the most optically dense substance highest refractive index.

Question 10.

1. A wall reflects light and a mirror also reflects light. What difference is there in the way they reflect light?
2. Which type of reflection of light leads to the formation of images?

Answer:

1. A wall has a rough surface, so the reflection by a wall is a diffuse reflection. On the other hand, a mirror surface is smooth, so the reflection by a mirror is a regular reflection,
2. Regular reflection

Question 11. Which type of mirror has:

1. Positive focal length?
2. Negative focal length?

Answer:

1. Convex mirror
2. Concave mirror

Question 12. Between which two points of concave mirror should an object be placed to obtain a magnification of:

1. -3
2. + 2.5

Answer:

1. Between focus and centre of curvature
2. Between pole and focus.

Question 13. If the focal length of a convex mirror is 15 cm, what is its radius of curvature?

Answer:

R = 30 cm

Question 14. The characteristics of image formed for an optical device are as follows:

1. To which spherical lens or mirror do the characteristics mentioned in the table belongs to?
2. What sign is assigned to the value of focal length of this lens or mirror according to New Cartesian sign convention?

Answer:

1. The characteristics mentioned in the given below belongs to the images formed by concave lens,
2. The diverging les or concave lens has negative focal length according to the New Cartesian sign convention.

Question 15. A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 24 cm. The distance of the object from the lens is 16 cm. Find the position, size and nature of the image formed, using the lens formula.

Answer:

Position of image: Image is formed at a distance of 48 cm from the optical centre of the lens on the same side of the object. It is indicated by the negative sign.

Size of image: It is three times the size of object, i.e. 12 cm.

Nature of image: Positive sign in the image height indicates that image is virtual and erect.

Question 16.

1. Under what condition will a glass lens placed in a transparent liquid become invisible?
2. Describe and illustrate with a diagram, how we should arrange two converging lenses so that a parallel beam of light entering one lens emerges as a parallel beam after passing through the second lens.

Answer:

1. When the refractive index of glass lens becomes equal to the refractive index of transparent liquid, the glass lens will become invisible,
2. Parallel beam converges at focus of the first lens and emerges parallel as it is at the focus of second lens, as shown in figure.

Question 17.

1. If the image formed by a lens is diminished in size and erect, for all positions of the object, what type of lens is it?
2. Name the point on the lens through which a ray of light passes undeviated.

Answer:

1. Concave lens
2. Optical centre

Question 18. The outer surface of a hollow sphere of aluminium of radius 50 cm is to be used as a mirror. What will be the focal length of this mirror? Which type of spherical mirror will it provide?

Answer:

f = R/2 = 25 cm. It will form a convex mirror.

Question 19. What is the nature of the image formed by a convex mirror when the object is placed between the pole and infinity?

1. What is diffused reflection of light?
2. Which mirror is used as a rear-view mirror? Why?

Answer:

1. When an object is placed between the pole and infinity, the image formed is virtual, erect and diminished,
2. When light rays are incident on the rough surface, they are reflected in different directions. This type of reflection is called diffused reflection or irregular reflection,
3. A convex mirror always produces an erect, virtual and diminished image. This enables a driver to view a much larger area behind him. Hence, a convex mirror is suitable as a rear-view mirror.

Question 20. State the signs (positive or negative) and give reasons which can be given to the following:

1. Object distance (u) for a concave mirror or convex mirror
2. Image distances (v) for a concave mirror
3. Image distances (v) for a convex mirror

Answer:

1. Object distance (u) for a concave mirror or convex mirror is always negative because an object is always placed to the left side of the mirror and the distances towards the left of the mirror are always negative,
2. In case of a concave mirror, if the image is formed on the left side of the mirror, then the image distance (v) will be negative and if the image is formed on the right side of the mirror, then the image distance (v) will be positive. This is because distances measured to the left of the mirror are negative and to the right of the mirror is positive,
3. Image distances (v) for a convex mirror is always positive because the image is always formed behind the mirror.

Question 21. A person got his eyes tested by an optician. The prescription for the spectacle lenses to be made reads:

Left eye: + 2.50 D; Right eye: + 2.00 D

1. State whether these lenses are thicker in the middle or at the edges.
2. Which lens bends the light rays more strongly?
3. State whether these spectacles lenses will converge light rays or diverge light rays.

Answer:

1. These lenses have positive powers and hence positive focal lengths, so they are convex lenses. Convex lenses are thicker in the middle,
2. Lens of greater power bends light rays more quickly. So, +2.50 D lens bends light rays more quickly,
3. These spectacle lenses will converge the light rays because these are convex lenses.

Question 22. The image of an object placed at 30 cm in front of a lens is obtained on a screen at a distance of 60 cm from it. Find the focal length of the lens. What would be the height of the image if the object is 2 cm high?

Answer:

Object distance, u = – 30 cm

Image distance, v = 60 cm

From the lens formula,

⇒ \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=\frac{1}{60}-\frac{1}{-30}=\frac{1}{60}+\frac{1}{30}=0.05\)

Therefore, f = 20 cm

Height of the object, h = 2 cm

From the magnification formula,

⇒ \(\mathrm{m}=\frac{\mathrm{v}}{\mathrm{u}}=\frac{\mathrm{h}^{\prime}}{\mathrm{h}}\)

Therefore, \(\mathrm{h}^{\prime}=\frac{\mathrm{v}}{\mathrm{u}} \mathrm{~h}=\frac{60}{-30} \times 2\)

h’ = -4 cm

Question 23. Refractive index of water with respect to air is 1.33 and that of diamond is 2.42.

1. In which medium does the light move faster, water or diamond?
2. What is the refractive index of diamond with respect to water?

Answer:

1. Refractive index = speed of light in vacuum / speed of light in medium.

The refractive index of diamond is more.

Thus, the speed of light is lesser in diamond. Hence, the light moves faster in water than in diamond.

2. Let speed of light in water be vw and that in diamond be vd.

Let refractive index of diamond w.r.t water = μ

Therefore, p = Speed of light in water / speed of light in diamond

P = V_w/V_d

P = (V_w/c) ÷ (v_d/c)μ = 2.42/1.33 = 1.82

Question 24. A 2 cm high object is placed at a distance of 20 cm from a concave mirror. A real image is formed at 40 cm from the mirror. Calculate the focal length of the mirror. Also, find the height of the image formed.

Answer:

Object distance, u = -20 cm

Image distance, v = -40 cm

Height of object (h0) = 2 cm

According to the mirror formula,

⇒ \(\frac{1}{v}+\frac{1}{u}=\frac{1}{f}\)

⇒ \(\frac{1}{-40}+\frac{1}{-20}=\frac{1}{f}\)

∴ \(\mathrm{f}=-\frac{4 0}{3}=-13.33 \mathrm{~cm}\)

Magnification, m = -v/u = h_image/h_object

-40/-20 = h_image/2

h_image= – 4 Cm

Question 25. The face of a person is 24 cm long and 20 cm wide. What is the minimum size of the mirror required to see the full face?

Answer:

The size of the mirror required to see the full face should be half the size of the face.

Hence, the mirror should be 24/2 = 12 cm long and 20/2 = 10 cm wide. Also, the mirror should be placed with the longer side vertical and the eyes kept at proper height.

Question 26. The image of an object placed at 25 cm in front of a concave mirror is obtained on a screen at a distance of 50 cm from it. Find the focal length of the lens. What would be the height of the image if the object is 2 cm high?

Answer:

Object distance, u = -25 cm

Image distance, v = -50 cm

From the mirror formula,

⇒ \(\frac{1}{\mathrm{f}}=\frac{1}{v}+\frac{1}{u}=\frac{1}{-50}+\frac{1}{-25}=-0.06\)

Therefore, f (focal length of mirror) = -16.66 cm

Height of the object, h = 2 cm

From the magnification formula,

⇒ \(m=-\frac{v}{u}=\frac{h 2}{h 1}\)

∴ \(\mathrm{h} 2=-\frac{\mathrm{v}}{\mathrm{u}} h 1=-\left(-\frac{50}{-25}\right) \times 2=-4 \mathrm{~cm}\)

Height of the image is 4 cm.

Question 27. An object 4 cm in size is placed at a distance of 8 cm from a convex mirror of radius of curvature 20 cm. Find the nature, position and size of the image.

Answer:

Object distance, u = 8 cm

Image distance (v) = ?

Focal length = f = R/2 = 10 cm

⇒ \(\frac{1}{10}=\frac{1}{v}+\frac{1}{-8}\)

⇒ \(\frac{1}{v}=\frac{1}{10}+\frac{1}{8}=\frac{18}{80}=0.225\)

v = +4.4 cm

Thus, the position of the image is 4.4 cm behind the convex mirror. As the image is formed behind the convex mirror, its nature will be virtual and erect.

Magnification of the convex mirror is

m =-v/u = -4.4/-8 = 0.55

Also, m = h2/h1

0.55 = h2/4

h2 = 2.2 cm; Thus, the size of the image is 2.2 cm.

Question 28. A concave mirror produces a three times larger real image of an object placed at a distance of 20 cm in front of it. Find the position of the image and the nature of the image. Also, find the focal length of the mirror.

Answer:

m = -3; u = -20 cm

m = -v/u

-3 = -v/ (-20)

v = -60 cm

The image is located at a distance of 60 cm, and the nature of the image is enlarged, real and inverted.

∴ \(\frac{1}{f}=\frac{1}{v}+\frac{1}{u}=\frac{1}{-60}+\frac{1}{-20}=-\frac{80}{1200}\)

f = -15 cm

Thus, the focal length of a concave mirror is 15 cm.

Question 29.

1. For what position of the object does a convex lens form an erect and virtual image?
2. What is regular reflection of light?
3. What type of mirror is used as a shaving mirror? Support your answer with a reason.

Answer:

1. When the object lies between the optical centre and the focus of the lens, a convex lens forms an erect and virtual image.
2. When a parallel beam of light falls on a smooth and highly polished surface, the reflected beam is also parallel and directed in a fixed direction. Such reflection of light is called regular reflection.
3. Concave mirrors are used as shaving mirrors to see a large image of the face. This is because when the face is held within the focus of a concave mirror, an enlarged image of the face is seen in the concave mirror. This helps in getting a smooth shave.

Question 30. What is the focal length of a concave mirror if the radius of curvature is 12 cm? What is the nature of the image formed by a concave mirror when an object is placed between its focus and pole? Draw the diagram for the same.

Answer:

R = -12 cm (Radius of curvature of a concave mirror)

We know that, f = R/2 = -12/2 =- 6 cm.

The image formed by a concave mirror when an object is placed between the focus and pole is virtual, erect and magnified.

Question 31. A ray of light is incident at an angle of 45° at the interface of medium (1) and medium (2) as shown in the above diagram. Redraw this diagram in the answer book and complete it. If the angle of refraction is 30°, find the refractive index of medium (2) with respect to medium (1).

(Given that sin 450 =1/ V2 sin and sin 30° =1/2)

If the second medium is water in place of medium (2), will the angle of refraction increase or decrease? Why? (Refractive index of water = 4/3)

Answer:

Using Snell’s law, the refractive index of medium (2) with respect to medium (1) is given as

∴ \(n 21=\frac{\sin i}{\sin r}=\sin 45^{\circ} / \sin 30^{\circ}=1.414\)

If the second medium is water in place of medium (2), the angle of refraction will decrease because water is rarer than medium (2).

Question 32.

1. What is meant by refraction of light?
2. One student measures the angle of refraction as 25° in medium A, and the other student measures the angle of refraction as 23° in the other medium B for the same angle of incidence 40°. Find the refractive index of both media. In which medium does light travel faster?

Answer:

1. When light travels from one transparent medium to another transparent medium, deviation of its path takes place at the boundary. When light rays enter from a rarer medium to a denser medium (For Example. air to glass), they deviate towards the normal drawn at the point of incidence on the boundary. When light rays emerge out of a denser medium to a rarer medium (For Example. glass to air), they deviate away from the normal drawn at the point of incidence on the boundary. This is known as refraction of light.
2. In medium A: Refractive index μ_A = sin (40°)/sin (25°) = 1.521.

In medium B: Refractive index μ_B = sin (40°)/sin (23°) = 1.645.

Refractive index (μ) of medium = c/v = velocity in air/ velocity in medium.

Hence, velocity in a medium is inversely proportional to the refractive index. So, light travels faster in medium A compared to medium B.

Question 33.

1. A girl was playing with a thin beam of light from her laser torch by directing it from different directions on a convex lens held vertically. She was surprised to see that in a particular direction the beam of light continues to move along the same direction after passing through the lens. State the reason for this observation.
2. Explain why a ray of light passing through the centre of curvature of a concave mirror, gets reflected along the same path.

Answer:

1. A ray of light passing through the optical centre of the convex lens will continue to move along the same direction after refracting through the lens.
2. The ray passing through the centre of curvature incident to the mirror along its normal so ∠i = ∠r = 0. Therefore, the ray retraces its path.

Question 34. Define refractive index. If light enters from air to glass having a refractive index 1.5, then calculate the speed of light in glass.

Answer:

The ratio of the speed of light in vacuum to the speed of light in a medium is called the refractive index of the medium.

n = Speed of light in air/ Speed of light in glass

1.5 = 3 x10⁸/ Speed of light in glass

Speed of light in glass = 3 x 10⁸/1.5 = 2.5 x 10⁸ ms^-1

Chapter 1 Light-Reflection And Refraction Long Questions And Answers

Question 1.

1. Name the type of mirrors used in

• A search light and
• Rear-view mirror. Draw labelled diagrams to show the formation of an image in each of these two cases.

2. Which of these mirrors could also form a magnified and virtual image of an object? Illustrate with the help of a ray diagram.

Answer:

1. The mirror used in a searchlight is a concave mirror. A light source is placed at the focal point of the mirror. Light rays from the source are reflected by the mirror and all the reflected rays are parallel so that they travel a long distance to help in search operations.

The mirror used as a rear-view mirror is a convex mirror. Image formed by a convex mirror is as follows:

2. A concave mirror can form a magnified and virtual image. A convex mirror cannot form an enlarged image. When the object is placed between the pole and the focus of the mirror, the image formed is virtual, enlarged and erect.

Question 2.

1. Define:

• Principal focus of a convex lens
• Optical centre

2. State the lens formula.

3. Magnification produced by a spherical lens is -1. What is the nature of the image and lens?

Answer:

• The principal focus of a convex lens is a point on its principal axis to which light rays parallel to the principal axis converge after passing through the lens.
• The centre point of the lens is known as the optical centre.

2. Lens Formula is \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\)

where”f is the focal length of the lens, “v” is the image distance and “u” is the object distance

3. Magnification of the lens = -1

Since magnification is negative, the image formed is real and inverted. Value 1 indicates that the size of the image is equal to the size of the object. Such an image can be formed by a convex lens. Hence, it is a convex lens.

Question 3.

1. What do you mean by linear magnification produced by mirrors?
2. The power of a lens is +1.5 D. What kind of lens is it and what is its focal length?
3. Draw a ray diagram of an image when an object is placed on the principal axis of a convex lens between the focus and the optical centre.

Answer:

1. The linear magnification produced by a mirror is defined as the ratio of the height of the image to the height of the object.

2. The power of the lens has a positive sign; so, it is a convex lens.

Power, \(P=\frac{1}{f}\)

∴ \(\mathrm{f}=\frac{1}{\mathrm{p}}=\frac{1}{2.5}\)

f = 0.4 m = 40 cm

3. When the object is between the focus and the optical centre of a convex lens, the image formed is

• Beyond the focus
• Virtual and erect
• Enlarged.

Question 4. Draw the ray diagram and state the nature and position of the image formed when the object is placed at

1. 2F in front of a convex lens
2. Anywhere between the optical centre and infinity of the concave lens

Answer:

1. When an object is placed at 2F in front of the convex lens:

Nature of the image is real, inverted and is of the same size as that of the object. Position of the image formed is at a distance of 2f on the other side of the image.

2. When an object is placed anywhere between the optical centre and infinity of the concave lens:

Nature of the image is virtual, erect and diminished. Position of the image is between the optical centre and the focus.

Question 5.

1. What is the mirror formula? Give an expression for the mirror formula.
2. Define the following terms related to spherical mirrors:
   • Pole
   • Centre of curvature
   • Principal axis

Answer:

1. The relation between the object distance (u), image distance (v) and focal length (f) of a spherical mirror is given by the mirror formula. The object distance (u), image distance (v) and focal length (f) of a spherical mirror are related as \(\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\)

2.

1. • The pole (P) of a spherical mirror is the centre of the mirror.

• • The centre of curvature (C) of a spherical mirror is the centre of the hollow sphere of glass, of which the spherical mirror is a part.
  • The principal axis of a spherical mirror is a straight line passing through the centre of curvature C and pole P of the spherical mirror.