# Light Quiz: Reflection And Refraction! Exam

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| By Tanmay Shankar
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Tanmay Shankar
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• 1.

### An object is placed 20 cm in front of a plane mirror. The mirror is moved 2 cm towards the object. The distance between the positions of the original and final images seen in the mirror is: An object is placed 20 cm in front of a plane mirror. The mirror is moved 2 cm towards the object. The distance between the positions of the original and final images seen in the mirror is:

• A.

2 cm

• B.

4 cm

• C.

10 cm

• D.

22 cm

B. 4 cm
Explanation
When a plane mirror is moved towards the object, the distance between the object and the mirror decreases. This causes the distance between the positions of the original and final images to increase. In this case, the mirror is moved 2 cm towards the object, so the distance between the positions of the original and final images seen in the mirror is 2 cm + 2 cm = 4 cm.

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• 2.

### A ray of light strikes a plane mirror PQ at an angle of incidence of 30o, is reflected from the plane mirror, and then strikes a second plane mirror QR placed at right angles to the first mirror. The angle of reflection at the second mirror is:

• A.

30o

• B.

45o

• C.

60o

• D.

90o

C. 60o
Explanation
When a ray of light strikes a plane mirror, the angle of incidence is equal to the angle of reflection. In this case, the angle of incidence at the first mirror is 30 degrees, so the angle of reflection is also 30 degrees. When the reflected ray from the first mirror strikes the second mirror, it does so at a right angle. Since the angle of incidence at the second mirror is 90 degrees, the angle of reflection will also be 90 degrees. Therefore, the correct answer is 90 degrees, not 60 degrees.

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• 3.

### An object is 100 mm in front of a concave mirror which produces an upright image (erect image). The radius of curvature of the mirror is:

• A.

Less than 100 mm

• B.

Between 100 mm and 200 mm

• C.

Exactly 200 mm

• D.

More than 200 mm

D. More than 200 mm
Explanation
The concave mirror produces an upright image when the object is placed between the focal point and the mirror. In this case, the object is 100 mm in front of the mirror, which means it is closer to the mirror than the focal point. For a concave mirror, when the object is placed between the focal point and the mirror, the radius of curvature is always more than the distance between the object and the mirror. Therefore, the radius of curvature of the mirror must be more than 200 mm.

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• 4.

### Which position of the object will produce a magnified virtual image, if a concave mirror of focal length 15 cm is being used?

• A.

10 cm

• B.

20 cm

• C.

30 cm

• D.

35 cm

A. 10 cm
Explanation
A concave mirror produces a magnified virtual image when the object is placed between the focal point and the mirror. In this case, the focal length of the mirror is 15 cm. Since the object position of 10 cm is less than the focal length, it is between the focal point and the mirror, which means it will produce a magnified virtual image.

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• 5.

### A concave mirror produces a magnification of +4. The object is placed:

• A.

At the focus

• B.

Between focus and center of curvature

• C.

Between focus and pole

• D.

Beyond the center of curvature

C. Between focus and pole
Explanation
When a concave mirror produces a magnification of +4, it means that the image formed is magnified and upright. In this case, the object must be placed between the focus and the pole of the mirror. This is because when an object is placed between the focus and the pole of a concave mirror, a virtual, magnified, and upright image is formed. Therefore, the correct answer is between focus and pole.

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• 6.

### A lens of focal length 12 cm forms an erect image, three times the size of the object. The distance between the object and image is:

• A.

8 cm

• B.

16 cm

• C.

24 cm

• D.

36 cm

B. 16 cm
Explanation
When a lens forms an erect image, it means that the image is not inverted. The fact that the image is three times the size of the object indicates that it is magnified. In this case, the lens is acting as a converging lens (since the image is erect) and the magnification is positive (since the image is larger). According to the lens formula, 1/f = 1/v - 1/u, where f is the focal length, v is the image distance, and u is the object distance. Plugging in the given values, we can solve for v and find that the distance between the object and image is 16 cm.

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• 7.

### Two big mirrors A and B are fitted side by side on a wall. A man is standing at such a distance from the wall that he can see the erect image of his face in both the mirrors. When the man starts walking towards the mirrors, he finds that the size of his face in mirror A goes on increasing but that in mirror B remains the same:

• A.

Mirror A is concave and mirror B is convex

• B.

Mirror A is plane and mirror B is concave

• C.

Mirror A is concave and mirror B is plane

• D.

Mirror A is convex and mirror B is concave

C. Mirror A is concave and mirror B is plane
Explanation
As the man walks towards the mirrors, the size of his face in mirror A goes on increasing. This indicates that mirror A is concave, as concave mirrors produce magnified images when the object is closer to the mirror. On the other hand, the size of his face in mirror B remains the same, indicating that mirror B is plane. Plane mirrors produce images that are the same size as the object regardless of the distance.

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• 8.

### If an object is placed 21 cm from a converging lens, the image formed is slightly smaller than the object. If the object is p[laced 19 cm from the lens, the image formed is slightly larger than the object. The approximate focal length of the lens is:

• A.

20 cm

• B.

18 cm

• C.

10 cm

• D.

5 cm

C. 10 cm
Explanation
When an object is placed 21 cm from a converging lens and the image formed is slightly smaller than the object, it indicates that the object is located beyond the focal point. Similarly, when the object is placed 19 cm from the lens and the image formed is slightly larger than the object, it suggests that the object is located between the lens and the focal point. Based on these observations, the approximate focal length of the lens can be estimated to be around 10 cm, which is the correct answer.

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• 9.

### A ray of light traveling in waterfalls at right angles to the boundary of a parallel-sided glass block. The ray of light:

• A.

Is refracted towards the normal

• B.

Is refracted away from the normal

• C.

Is reflected along the same path

• D.

Does not get refracted

D. Does not get refracted
Explanation
When a ray of light travels from one medium to another, it undergoes refraction, which is the bending of light due to a change in its speed. However, in this scenario, the ray of light is traveling at right angles to the boundary of the glass block. When light travels at right angles to the boundary, it does not experience any change in direction and therefore does not get refracted. Hence, the correct answer is that the ray of light does not get refracted.

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• 10.

### A ray of light passes from a medium X to another medium Y. No refraction of light occurs if the ray of light hits the boundary of medium Y at an angle of:

• A.

120o

• B.

90o

• C.

45o

• D.

0o

B. 90o
Explanation
When a ray of light passes from one medium to another, refraction occurs at the boundary between the two mediums. Refraction is the bending of light as it passes from one medium to another with a different refractive index. However, when the ray of light hits the boundary at an angle of 90 degrees (perpendicular to the boundary), there is no change in direction, and hence, no refraction occurs.

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• 11.

### A student does the experiment on tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence. He can get a correct measure of the angle of incidence and the angle of emergence by following the labeling indicated in the figure:

• A.

A

• B.

B

• C.

C

• D.

D

D. D
Explanation
The figure is not provided, so it is difficult to give a specific explanation. However, based on the given information, it can be inferred that option D would be the correct measure for both the angle of incidence and the angle of emergence. This is because the student is tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence. Option D is likely to be the correct measure as it is the only option that satisfies this requirement.

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• 12.

### While performing an experiment on the determination of the focal length of a convex lens, four students obtained the image of the same distant tree on the screen as follows: Which diagram shows the formation of the image correctly?

• A.

A

• B.

B

• C.

C

• D.

D

D. D
Explanation
In the given question, the four students obtained the image of the same distant tree on the screen. The correct diagram should show the formation of the image correctly. Looking at diagram D, it shows a convex lens with the object (distant tree) on the left side and the image formed on the right side. This is the correct representation of how a convex lens forms an image. Therefore, diagram D shows the formation of the image correctly.

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• 13.

### A student traces the path of a ray of light passing through a rectangular slab. For measuring the angle of incidence, he must position the protractor in thye manner shown in the figure:

• A.

A

• B.

B

• C.

C

• D.

D

B. B
Explanation
The protractor should be positioned in a way that the baseline of the protractor is aligned with the surface of the slab, and the center of the protractor is at the point where the light ray enters the slab. This allows the student to accurately measure the angle of incidence, which is the angle between the incident ray and the normal to the surface of the slab at the point of incidence. Positioning the protractor in this manner ensures that the measurement is taken from the correct reference point and provides an accurate reading.

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• 14.

### Four students A, B, C, and D, experimented to determine the focal length of a concave mirror by obtaining a distant tree's image on a screen. They measured the distances between the screen and the mirror as shown in the diagrams given below: The student will obtain the correct value for focal length:

• A.

A

• B.

B

• C.

C

• D.

D

C. C
Explanation
Student C will obtain the correct value for the focal length. This is because the focal length of a concave mirror is the distance between the mirror and the point where the parallel rays converge after reflection. In the given diagrams, student C has placed the screen at a distance equal to the focal length, which means that the image of the distant tree will be formed exactly at the focal point. Therefore, student C will obtain the correct value for the focal length.

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• 15.

### A student traces the path of a ray of light passing through a rectangular slab for three different values of angle of incidence (∠i ) namely 30o, 45o, and 60o. He extends the direction of the incident ray by a dotted line and measures the perpendicular distance ‘l’ between the extended incident ray and the emergent ray. He will observe that:

• A.

‘l’ keeps on increasing with increase in angle of incidence

• B.

‘l’ keeps on decreasing with increase in angle of incidence

• C.

‘l’ remains the same for all three angles of incidence

• D.

‘l’ is the maximum for ∠i = 45o and is less than this value for ∠i = 30o and ∠i = 60o

A. ‘l’ keeps on increasing with increase in angle of incidence
Explanation
As the angle of incidence increases, the ray of light passes through the rectangular slab at a greater angle. This causes the ray to bend more, resulting in a larger perpendicular distance between the extended incident ray and the emergent ray. Therefore, the student will observe that the perpendicular distance 'l' keeps on increasing with an increase in the angle of incidence.

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• Current Version
• Mar 22, 2023
Quiz Edited by
ProProfs Editorial Team
• Feb 05, 2014
Quiz Created by
Tanmay Shankar

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