CDS Questions on Light, Lenses and Mirrors

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CDS 2020-I

1. Which one of the following is NOT true about the image formed by a plane mirror?

  1. It is of the same size as the subject.
  2. It is laterally inverted.
  3. It is real image.
  4. It is formed as far behing the mirror as the object is in front.

2. In a periscope, the two plane mirrors are kept

  1. parallel to each other
  2. perpendicular to each other
  3. at an angle of 60o with each other
  4. at an angle of 45o with each other

3. If the speed of light in air is 3 x 108 m/s, then the speed of light in a medium of refractive index 3/2 is

  1. 2 x 108
  2. (9/4) x 108
  3. (3/2) x 108
  4. 3 x 108

CDS 2020-II

4. Which one of the following statements with regard to the ultraviolet light is NOT correct?

  1. It is an electromagnetic wave.
  2. It can travel through vacuum.
  3. It is a longitudinal wave.
  4. Its wavelength is shorter/smaller than that of visible light.

5. If the speed of light in air is represented by c and the speed in a medium is v, then the refractive index of the medium can be calculated using the formula

  1. v/c
  2. c/v
  3. c/(2.v)
  4. (c - v)/c

6. Which of the following lenses will bend the light rays through largest angle?

  1. Lens with power +2.0 D
  2. Lens with power +2.5 D
  3. Lens with power -1.5 D
  4. Lens with power -2.0 D

7. A luminous object is placed at a distance of 40 cm from a converging lens of focal length 25 cm. The image obtained the screen is

  1. erect and magnified
  2. erect and smaller
  3. inverted and magnified
  4. inverted and smaller

8. When a light ray enters into glass medium from water at an angle of incidence 0o, what would be the angle of refraction?

  1. 90o
  2. 45o
  3. 0o
  4. The ray will not enter at all

9. Which one of the following phenomena verifies the fact that light travels much faster than sound?

  1. Twinkling of stars in night sky
  2. Lighting of matchstick
  3. Thunderstorm
  4. Mirage

10. Which one of the following combinations of source and screen would produce sharpest shadow of an opaque object?

  1. A point source and an opaque screen
  2. An extended source and an opaque screen
  3. A point source and a transparent screen
  4. An extended source and a transparent screen

CDS 2021-I

11. A non-spherical shining spoon can generally be considered as a

  1. Spherical mirror
  2. Parabolic mirror
  3. Plane mirror
  4. Lens

12. How many internal reflections of light take place in the formation of primary rainbow?

  1. 0
  2. 1
  3. 2
  4. More than 2

CDS 2021-II

13. Where should an object be placed in front of a convex lens to get a real and enlarged image of the object?

  1. At twice the focal length
  2. At infinity
  3. Between the principal focus and twice the focal length
  4. Beyond twice the focal length

14. A ray of light travelling from a rarer medium to a denser medium

  1. slows down and bends away from the normal
  2. slows down and bends towards from the normal
  3. speeds up and bends away from the normal
  4. speeds up and bends towards from the normal

15. Refraction of light, as it enters from one transparent medium to another, is due to

  1. change in temperature of the media.
  2. change in the amplitude of light.
  3. change in speed of light.
  4. internal property of light.

CDS 2022-I

16. If the magnification produced by a lens is +2, then the image is:

  1. erect, virtual and smaller than the object
  2. inverted, real and smaller than the object
  3. erect, virtual and larger than the object
  4. inverted, real and larger than the object

17. The twinkling of a star is due to:

  1. atmospheric reflection of starlight.
  2. atmospheric refraction of starlight.
  3. continuous change in the position of the star.
  4. oscillation of starlight.

18. A convex lens has a focal length of 15 cm. At what distance should an object be placed in front of the lens to get a real image of the same size of the object?

  1. 15 cm
  2. 10 cm
  3. 30 cm
  4. 40 cm

CDS 2022-II

19. If an object is placed at the focus of a convex lens, its image is

  1. at the focus on the same side.
  2. at the focus on the opposite side
  3. coincident with the lens
  4. at infinity

20. Which one of the following statements about the aperture of a convex lens is correct?

  1. It is equal to its radius of curvature.
  2. It is equal to its focal length.
  3. It is independent of its radius of curvature.
  4. It is equal to half of its focal length.

CDS 2023-I

21. The power of a lens of focal length 10 cm is

  1. 0.1 dioptre
  2. 1 dioptre
  3. 10 dioptre
  4. 100 dioptre

CDS 2023-II

22. A concave mirror of radius of curvature 50 cm is used to form an image of an object kept at a distance of 25 cm from the mirror on its principal axis. What will be the position of the image from the mirror?

  1. At infinity
  2. At 50 cm
  3. At 25 cm
  4. At 75 cm

23. Which one of the following statements is correct regarding the travel of a light beam from a rare to a dense medium?

  1. A light beam travelling from a rare medium to a dense medium slows down and bends towards the normal.
  2. A light beam travelling from a rare medium to a dense medium speeds up and bends towards the normal.
  3. A light beam travelling from a rare medium to a dense medium slows down and bends away from the normal.
  4. A light beam travelling from a rare medium to a dense medium speeds up and bends away from the normal

CDS Solved Papers

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