Light

1

Two convex lenses with power 2 dioptre are kept in contact with each other. The focal length of the combined lens system is

  1. 0.10 m
  2. 2 m
  3. 4 m
  4. 0.25 m
2

Which one of the following statements about the refractive index of a material medium with respect to air is correct?

  1. It can be either positive or negative.
  2. It can have zero value.
  3. It is unity for all materials.
  4. It is always greater than one.
3

Which one of the following is the natural phenomenon based on which a simple periscope works?

  1. Reflection of light
  2. Refraction of light
  3. Dispersion of light
  4. Total internal reflection of light
4

A myopic person has a power of -1.25 Dioptre. What is the focal length and nature of his lens?

  1. 50 cm and convex lens
  2. 80 cm and convex lens
  3. 50 cm and concave lens
  4. 80 cm and concave lens
5

Which one of the following processes explains the splitting of a beam of white light into its constituent colours?

  1. Polarization
  2. Dispersion
  3. Diffraction
  4. Reflection
6

Consider the following statements:

A real image

  1. can be formed on a screen
  2. is always magnified and inverted

Which of the statements given above is/are correct

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
7

An optician prescribes a power = - 0.5 dioptre. The corresponding lens must be a

  1. convex lens of focal length 2 m
  2. concave lens of focal length 50 cm
  3. concave lens of focal length 2 m
  4. convex lens of focal length 50 cm
8

If the speed of light in air is 3 x 108 m/s, the speed of light in glass (with refractive index 1.5) would be

  1. 4.5 x 108 m/s
  2. 1.5 x 108 m/s
  3. 2 x 108 m/s
  4. 3 x 108 m/s
9

While looking at the image formed by a convex lens (one half of the lens is covered with black paper), which one of the following will happen to the image?

  1. Half of the image will be visible
  2. One can see an image of smaller size
  3. Intensity of the image will be diminished
  4. Image will be inverted
10

A person standing in front of a plane mirror approaches the mirror by 40 cm. The new distance between the person and his image in the plane mirror is

  1. 60 cm
  2. 1.4 m
  3. 1.2 m
  4. 2.0 m
11

An optical illusion which occurs mainly in deserts during hot summer is based on the principle of

  1. Reflection
  2. Interference
  3. Dispersion
  4. Total internal reflection
12

A rainbow is produced due to which one of the following phenomena?

  1. Dispersion of light
  2. Interference of light
  3. Diffraction of light
  4. Scattering of light by atmospheric dust
13

Concave mirror is used in headlights of vehicles, because it

  1. focuses light from the bulb onto nearby vehicles
  2. sends parallel rays
  3. fits well into the shape of the headlight
  4. is cheaper than other mirrors
14

The mirrors used as rear-view mirrors in vehicles are

  1. concave
  2. convex
  3. cylindrical
  4. plane
15

How long does light take to reach the Earth from the Sun?

  1. About 4 minutes
  2. About 8 minutes
  3. About 24 minutes
  4. About 24 hours
16

The focal length of the eye lens increases when eye muscles

  1. are relaxed and lens becomes thinner
  2. contract and lens becomes thicker
  3. are relaxed and lens becomes thicker
  4. contract and lens becomes thinner
17

When light rays enter the eye, most of the refraction occurs at the

  1. crystalline lens
  2. outer surface of the cornea
  3. iris
  4. pupil
18

The bluish colour of water in deep sea is due to

  1. the presence of algae and other plants found in water
  2. reflection of sky in water
  3. scattering of light
  4. absorption of light by the sea
19

Which of the following phenomena contributes significantly to the reddish appearance of the sun at sunrise or sunset?

  1. Dispersion of light
  2. Scattering of light
  3. Total internal reflection of light
  4. Reflection of light from the earth
20

The clear sky appears blue because

  1. blue light gets absorbed in the atmosphere
  2. ultraviolet radiations are absorbed in the atmosphere
  3. violet and blue lights get scattered more than lights of all other colours by the atmosphere
  4. light of all other colours is scattered more than the violet and blue colour lights by the atmosphere
21

Twinkling of stars is due to atmospheric

  1. dispersion of light by water droplets
  2. refraction of light by different layers of varying refractive indices
  3. scattering of light by dust particles
  4. internal reflection of light by clouds
22

Which of the following phenomena of light are involved in the formation of a rainbow?

  1. Reflection, refraction and dispersion
  2. Refraction, dispersion and total internal reflection
  3. Refraction, dispersion and internal reflection
  4. Dispersion, scattering and total internal reflection
23

At noon the sun appears white as

  1. light is least scattered
  2. all the colours of the white light are scattered away
  3. blue colour is scattered the most
  4. red colour is scattered the most
24

A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power

  1. + 0.5 D
  2. – 0.5 D
  3. + 0.2 D
  4. – 0.2 D
25

A full length image of a distant tall building can definitely be seen by using

  1. a concave mirror
  2. a convex mirror
  3. a plane mirror
  4. both concave as well as plane mirror
26

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. 15 cm in front of the mirror
  2. 30 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
27

Magnification produced by a rear view mirror fitted in vehicles

  1. is less than one
  2. is more than one
  3. is equal to one
  4. can be more than or less than one depending upon the position of the object in front of it
28

A light ray enters from medium A to medium B as shown in Figure.

The refractive index of medium B relative to A will be

  1. greater than unity
  2. less than unity
  3. equal to unity
  4. zero
29

A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is

  1. – 30 cm
  2. – 20 cm
  3. – 40 cm
  4. – 60 cm
30

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
31

Two mirrors A and B are placed at right angles to each other as shown in Figure.

A ray of light incident on mirror A at an angle of 25° falls on mirror B after reflection. The angle of reflection for the ray reflected from mirror B would be

  1. 25°
  2. 50°
  3. 65°
  4. 115°
32

A small hole P is made in a piece of cardboard. The hole is illuminated by a torch as shown in Figure. The pencil of light coming out of the hole falls on a mirror.

 

At which point should the eye be placed so that the hole can be seen?

  1. A
  2. B
  3. C
  4. D
33

Part of the eye which controls the light entering is called

  1. iris
  2. cornea
  3. lens
  4. retina
34

An erect and enlarged image can be formed by

  1. only a convex mirror
  2. only a concave mirror
  3. only a plane mirror
  4. both convex and concave mirrors
35

If an object is placed at a distance of 0.5 m in front of a plane mirror, the distance between the object and the image formed by the mirror will be

  1. 2 m
  2. 1 m
  3. 0.5 m
  4. 0.25 m
36

Which of the following can be used to form a real image?

  1. Concave mirror only
  2. Plane mirror only
  3. Convex mirror only
  4. Both concave and convex mirrors