Optics Question Bank

OPTICS 1.

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The light reflected by a plane mirror may form a real image (a) If the rays incident on the mirror are diverging (b) If the rays incident on the mirror are converging (c) If the object is placed very close to the mirror (d) Under no circumstances Two plane mirrors are inclined at an angle of 720 . The number of images of a point object placed between them will be (a) 2 (b) 3 (c) 4 (d) 5 To get three images of a single object, one should have two plane mirrors at an angle of (a) 30째 (b) 60째 (c) 90째 (d) 150째 A man of length h requires a mirror, to see his own complete image of length at least equal to h h h (a) (b) (c) (d) h 4 3 2 Two plane mirrors are at 45 to each other. If an object is placed between them, then the number of images will be (a) 5 (b) 9 (c) 7 (d) 8 A convex mirror of focal length f forms an image which is

1 n

times the object. The distance of the

object from the mirror is

n 1 n 1 f f (c) (d) (n 1) f n n A diminished virtual image can be formed only in (a) Plane mirror (b) A concave mirror (c) A convex mirror (d) Concave-parabolic mirror Which of the following could not produce a virtual image (a) Plane mirror (b) Convex mirror (c) Concave mirror (d) All the above can produce a virtual image An object 5cm tall is placed 1m from a concave spherical mirror which has a radius of curvature of 20 cm The size of the image is (a) 0.11cm (b) 0.50 cm (c) 0.55 cm (d) 0.60 cm The focal length of a concave mirror is 50 cm. Where an object be placed so that its image is two times and inverted (a) 75 cm (b) 72 cm (c) 63 cm (d) 50 cm An object of size 7.5cm is placed in front of a convex mirror of radius of curvature 25 cm at a distance of 40 cm. The size of the image should be (a) 2.3cm (b) 1.78cm (c) 1cm (d) 0.8cm The field of view is maximum for (a) Plane mirror (b) Concave mirror (c) Convex mirror (d) Cylindrical mirror The focal length of a concave mirror is f and the distance from the object to the principle focus is x.

The ratio of the size of the image to the size of the object is (a) (n 1) f

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(a) 14.

f

x f

(b)

(b)

f x

Image formed by a convex mirror is (a) Virtual (b) Real

(c)

f x

(c) Enlarged

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(d)

f2 x2

(d) Inverted

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In a concave mirror experiment, an object is placed at a distance x 1 from the focus and the image is formed at a distance x 2 from the focus. The focal length of the mirror would be x1 x1 x 2 (d) x2 2 A convex mirror is used to form the image of an object. Then which of the following statements is wrong (a) The image lies between the pole and the focus (b) The image is diminished in size (c) The image is erect (d) The image is real Given a point source of light, which of the following can produce a parallel beam of light (a) Convex mirror (b) Concave mirror (c) Concave lens (d) Two plane mirrors inclined at an angle of 90 The image formed by a convex mirror of focal length 30 cm is a quarter of the size of the object.

The distance of the object from the mirror is (a) 30 cm (b) 90 cm (c) 120 cm (d) 60 cm A boy stands straight infront of a mirror at a distance of 30 cm away from it. He sees his erect image 1 whose height is th of his real height. The mirror he is using is 5 (a) Plane mirror (b) Convex mirror (c) Concave mirror (d) Plano-convex mirror A person sees his virtual image by holding a mirror very close to the face. When he moves the mirror away from his face, the image becomes inverted. What type of mirror he is using (a) Plane mirror (b) Convex mirror (c) Concave mirror (d) None of these Which one of the following statements is true (a) An object situated at the principle focus of a concave lens will have its image formed at infinity (b) Concave mirror can give diminished virtual image (c) Given a point source of light, a convex mirror can produce a parallel beam of light (d) The virtual image formed in a plane mirror can be photographed The relation between the linear magnification m, the object distance u and the focal length f is

(a) x1x 2 16.

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(a) m 23.

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(b)

f

u f

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x1 x 2

(b) m

f f

u

(c) m

f

u f

(d) m

f f

u

While using an electric bulb, the reflection for street lighting should be from (a) Concave mirror (b) Convex mirror (c) Cylindrical mirror (d) Parabolic mirror A concave mirror is used to focus the image of a flower on a nearby well 120 cm from the flower. If a lateral magnification of 16 is desired, the distance of the flower from the mirror should be (a) 8cm (b) 12 cm (c) 80 cm (d) 120 cm A virtual image larger than the object can be obtained by (a) Concave mirror (b) Convex mirror (c) Plane mirror (d) Concave lens By corpuscular theory of light, the phenomenon which can be explained is (a) Refraction (b) Interference (c) Diffraction (d) Polarisation According to corpuscular theory of light, the different colours of light are due to (a) Different electromagnetic waves (b) Different force of attraction among the corpuscles (c) Different size of the corpuscles

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(d) None of the above Huygen's conception of secondary waves (a) Allow us to find the focal length of a thick lens (b) Is a geometrical method to find a wavefront (c) Is used to determine the velocity of light (d) Is used to explain polarisation The idea of the quantum nature of light has emerged in an attempt to explain (a) Interference (b) Diffraction (c) Radiation spectrum of a black body (d) Polarisation Two coherent sources of light can be obtained by (a) Two different lamps (b) Two different lamps but of the same power (c) Two different lamps of same power and having the same colour (d) None of the above

By Huygen's wave theory of light, we cannot explain the phenomenon of (a) Interference (b) Diffraction (c) Photoelectric effect (d) Polarisation The phenomenon of interference is shown by (a) Longitudinal mechanical waves only (b) Transverse mechanical waves only (c) Electromagnetic waves only (d) All the above types of waves Two coherent monochromatic light beams of intensities I and 4I are superposed. The maximum and minimum possible intensities in the resulting beam are (a) 5I and I (b) 5I and 3I (c) 9I and I (d) 9I and 3I Light appears to travel in straight lines since (a) It is not absorbed by the atmosphere (b) It is reflected by the atmosphere (c) Its wavelength is very small (d) Its velocity is very large The idea of secondary wavelets for the propagation of a wave was first given by (a) Newton (b) Huygen (c) Maxwell (d) Fresnel By a monochromatic wave, we mean (a) A single ray (b) A single ray of a single colour (c) Wave having a single wavelength (d) Many rays of a single colour The similarity between the sound waves and light waves is (a) Both are electromagnetic waves (b) Both are longitudinal waves (c) Both have the same speed in a medium (d) They can produce interference The ratio of intensities of two waves is 9 : 1. They are producing interference. The ratio of maximum and minimum intensities will be (a) 10 : 8 (b) 9 : 1 (c) 4 : 1 (d) 2 : 1 A wave can transmit ...... from one place to another (a) Energy (b) Amplitude (c) Wavelength (d) Matter If the ratio of intensities of two waves is 1 : 25, then the ratio of their amplitudes will be (a) 1 : 25 (b) 5 : 1 (c) 26 : 24 (d) 1 : 5 Two identical light sources S1 and S2 emit light of same wavelength . These light rays will exhibit interference if (a) Their phase differences remain constant (b) Their phases are distributed randomly (c) Their light intensities remain constant (d) Their light intensities change randomly Wave nature of light follows because (a) Light rays travel in a straight line (b) Light exhibits the phenomena of reflection and refraction (c) Light exhibits the phenomenon of interference

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(d) Light causes the phenomenon of photoelectric effect If L is the coherence length and c the velocity of light, the coherent time is L c 1 (a) cL (b) (c) (d) c L Lc If the amplitude ratio of two sources producing interference is 3 : 5, the ratio of intensities at maxima and minima is (a) 25 : 16 (b) 5 : 3 (c) 16 : 1 (d) 25 : 9 On a rainy day, a small oil film on water show brilliant colours. This is due to (a) Dispersion of light (b) Interference of light (c) Absorption of light (d) Scattering of light For constructive interference to take place between two monochromatic light waves of wavelength , the path difference should be

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(a) (2n 1)

(b) (2n 1) (c) n (d) (2n 1) 2 4 2 Two sources of waves are called coherent if (a) Both have the same amplitude of vibrations (b) Both produce waves of the same wavelength (c) Both produce waves of the same wavelength having constant phase difference (d) Both produce waves having the same velocity Soap bubble appears coloured due to the phenomenon of (a) Interference (b) Diffraction (c) Dispersion (d) Reflection Which of the following statements indicates that light waves are transverse (a) Light waves can travel in vacuum (b) Light waves show interference (c) Light waves can be polarized (d) Light waves can be diffracted If two light waves having same frequency have intensity ratio 4 : 1 and they interfere, the ratio of maximum to minimum intensity in the pattern will be (a) 9 : 1 (b) 3 : 1 (c) 25 : 9 (d) 16 : 25

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ANSWERS 1

b

2

c

3

c

4

c

5

c

6

a

7

c

8

d

9

c

10

a

11

b

12

c

13

b

14

a

15

b

16

d

17

b

18

b

19

b

20

c

21

d

22

b

23

b

24

a

25

a

26

a

27

c

28

b

29

c

30

d

31

c

32

d

33

c

34

c

35

b

36

a

37

d

38

c

39

a

40

d

41

a

42

c

43

b

44

c

45

b

46

c

47

c

48

a

49

c

50

a

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