CHAPTER 23 Wave-Optics (Interference, Diffraction

1. Huygens’ concepts of secondary waves *

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(a) allow us to find the focal length of a thin lens

(b) gives the magnifying power of a microscope

(c) is a geometrical method to find a wavefront

(d) is used to determine the velocity of light

2. The concept of secondary wavelets from all points on a wavefront was first proposed by *

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(a) Newton

(b) Huygen

(c) Faraday

(d) Raman

3. The wavefront is a surface in which *

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(a) all points are in the same phase

(b) there are pairs of points in opposite phase

(c) there are pairs of points with phase difference (p/2)

(d) there is no relation between the phases

4. Two light sources are coherent when *

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a) their amplitudes are equal

(b) their frequencies are equal

(c) their wavelengths are equal

(d) their frequencies are equal and their phase difference is constant

5. Newton has postulated his corpuscular theory on the basis of *

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(a) Newton’s ring

(b) colour due to thin film

(c) dispersing of light

(d) rectilinear propagation of ligh

6. Which of the following pairs denote coherent sources? *

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(a) Two pinholes infront of a broad sodium lamp

(b) Two pinholes infront of two identical sodium lamps

(c) Two pinholes infront of a laser beam

(d) All of the above

7. Two waves are said to be coherent if they have *

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(a) same amplitude

(b) same wavelength

(c) same amplitude and same wavelength

(d) same wavelength and constant phase difference

8. Two light waves are coherent if they are obtained from a single monochromatic source by *

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(a) division of amplitude only

(b) division of wavefront only

(c) both of the above

(d) none of the above

9. In the phenomenon of interference, the energy *

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(a) conservation does not hold good as energy is redistributed from destructive interference regions to

(b) conservation is valid, only redistribution of energy takes place

(c) conservation is not valid but amplitude addition holds good

(d) conservation is not valid but intensity addition Option 8

10. The necessary condition for an interference by two sources of light is that *

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(a) two light sources must have the same wavelength

(b) two point sources should have the same amplitude and same wavelength

(c) two sources should have the same wavelength, nearly the same amplitude and have a constant

(d) the two point sources should have a randomly varying phase differences

11. Two independent monochromatic sources are said to be incoherent, because the detector of light intensity requires time to detect intensity at a given position, that is *

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(a) much greater than 10–8 sec

(b) nearly equal to 10–8 sec

(c) much less than 10–8 sec

(d) none of the above

12. Two coherent monochromatic light beams of intensities I and 4I are superposed; the maximum and minimum possible intensities in the resulting beam are *

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(a) 5I and I

(b) 5I and 3I

(c) 9I and I

(d) 9I and 3I

13. If two waves, each of intensity I o , having the same frequency but differing by a constant phase angle of 60º, superpose at a certain point in space, then the intensity of resultant wave is *

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(a) 2Io

(b) 3Io

(c) 3Io

(d) 4Io

14. The light waves from two independent monochromatic light sources are given by y1 = 2 sin wt and y2 = 3 cos wt, then the correct statement is *

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(a) Both the waves are coherent

(b) Both the waves are incoherent

(c) Both the waves have different time periods

(d) None of the above

15. Two monochromatic waves each of intensity I have a constant phase difference of f. If these waves superpose, then the intensity of the resultant wave is *

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(a) 4I

(b) 4I cos f

(c) 4I cos2 f

(d) 4Io cos2 (f/2)

16. If the two waves represented by y1 = 4 sin wt and y2 = 3 sin (wt + p/3) interfere at a point, the amplitude of the resulting wave will be about *

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(a) 7

(b) 5

(c) 6

(d) 3.5

17. Four light sources produce the following four waves (i) y1 = a sin (wt + f1 ) (ii) y2 = a sin 2wt (iii) y3 = a′ sin (wt + f2 ) (iv) y4 = a′ sin (3wt + f) Superposition of which two waves give rise to interference? *

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(a) (i) and (ii)

(b) (ii) and (iii)

(c) (i) and (iii)

(d) (iii) and (iv)

18. For distructive interference the phase difference between the interfering waves should be *

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(a) 0, 2p, 4p, 6p, …

(b) p, 3p, 5p, 7p, …

(c) only zero phase difference

(d) p/2. 3p/2.5p/2, 7p/2

19. The distinguishable characteristic of a monochromatic light wave irrespective of medium is *

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(a) wavelength

(b) velocity

(c) intensity

(d) frequency

20. Select the right option in the following *

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(a) Christian Huygens, a contemporary of Newton established the wave theory of light by assuming

(b) Maxwell provided the theoretical evidence that light is transverse wave

(c) Thomas Young experimentally proved the wave behaviour of light and Huygens assumption

(d) All the statements given above, correctly answers the question “what is light”

21. The wave front of a distant source of unknown shape is approximately *

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(a) spherical

(b) cylindrical

(c) elliptical

(d) plane

22. In the Young’s double slit experiment, if monochromatic light used is replaced by white light, then *

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(a) no fringes are observed

(b) all bright fringes become white

(c) all bright fringes have colours between violet and red

(d) only central fringe is white and all other fringes are coloured

23. In Young’s double slit experiment, if width (aperture) of the slit S is increased keeping other parameters constant, then the interference fringes w *

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(a) remain unchanged

(b) from closer

(c) form further away

(d) gradually disappear

24. The contrast in the fringes in any interference pattern depends on *

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(a) fringewidth

(b) wavelength

(c) intensity ratio of the sources

(d) distance between the sources

25. In Young’s double slit experiment the separation between the slits is halved and the distance between the slits and screen is doubled. The fringe width is *

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(a) unchanged

(b) halved

(c) doubled

(d) quadrupled

26. In a Young’s double slit experiment, the fringe width is found to be 0.4 mm. If the whole apparatus is immersed in water of refractive index (4/3), without disturbing the geometrical arrangement, the new fringe width will be *

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(a) 0.30 mm

(b) 0.40 mm

(c) 0.53 mm

(d) 450 microns

27. Interference fringes of light are observed in an interference chamber containing pure water (m = 4/3). Now, if the water is drained out first and then the chamber is evacuated, then *

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(a) no interference fringe pattern is observed

(b) same interference fringe pattern is observed

(c) interference pattern with smaller fringe width is observed

(d) interference pattern with larger fringe width is observed

28. Interference was observed in an interference chamber, when air was present. Now, the chamber is evacuated and if the same light is used, a careful observation will show *

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(a) no interference

(b) interference with bright bands

(c) interference with dark bands

(d) interference in which breadth of the fringe will be slightly increased

29. Interference of light waves from two coherent sources is possible for *

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(a) unpolarised light waves only

(b) polarised light waves only if their polarisation is in the same direction

(c) both of the above

(d) none of the above

30. In a two slit experiment with white light, a white fringe is observed on a screen kept behind the slits. When the screen is moved away by 0.05 m, this white fringe *

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(a) does not move at all

(b) gets displaced from its earlier position

(c) becomes coloured

(d) disappears

31. For best contrast between maxima and minima in the interference pattern of Young’s double slit experiment, the intensity of light emerging out of the two slits should be *

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(a) equal

(b) double

(c) small

(d) large

32. The angular fringe width of fringes formed with sodium light of wavelength 5890 Å is 0.20º. If the whole arrangement is immersed in water, then the angular width of the fringes will become *

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(a) 0.11º

(b) 0.15º

(c) 0.22º

(d) 0.30º

33. The double slit experiment of Young has been shown in the figure. Q is the position of the first bright fringe on the right side and P is the 11th fringe on the other side as measured from Q. If wavelength of light used is 6000 Å, S1 B will be equal to *

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(a) 6 × 10–6 m

(b) 6.6 × 10–6 m

(c) 3.138 × 10–7 m

(d) 3.144 × 10–7 m

34. Yellow light emitted by sodium lamp in Young’s double slit experiment is replaced by monochromatic blue light of the same intensity *

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(a) fringe width will decrease

(b) fringe width will increase

(c) fringe width will remain unchanged

(d) fringes will become less intense

35. In a Young’s double slit experimental arrangement shown here, if a mica sheet of thickness t and refractive index m is placed in front of the slit S1 , then the path difference (S1 P – S2 P) *

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(a) decreases by (m – 1)t

(b) increases by (m – 1)t

(c) does not change

(d) increases by mt

36. In Young’s experiment monochromatic light is used to illuminate the two slits A and B. Interference fringes are observed on a screen placed in front of the slits. Now, if a thin glass plate is placed normally in the path of the beam coming from the slit A, then *

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(a) the fringes will disappear

(b) the fringes width will increase

(c) the fringe width will decrease

(d) there will be no change in fringe width but fringe pattern shifts

37. The interference fringes pattern, in Young’s double slit experiment, will not be observed if *

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(a) the separation d between the two slits is of the order of l

(b) the separation d between the two slits is very large of the order of a metre

(c) the width of the slit S is large of the order of a few mm

(d) all of the above

38. If a thin mica sheet of thickness t and refractive index m is placed in the path of one of the waves producing interference, then the whole interference pattern shifts towards the side of the sheet by a distance *

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(a) d /D ( ) m − 1 t

(b) D/d ( ) m − 1 t

(c) Dd(m – 1)t

(d) (m – 1)t

39. In Young’s double slit experiment, white light source is used to obtain a white central fringe and a few coloured fringes. Now if a filter allowing only red light is used in front of slit S1 and another filter allowing only blue light is used in front of second slit S2 , then *

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(a) only red coloured fringes will be observed

(b) only blue colourd fringes will be observed

(c) both red coloured and blue coloured fringes will be observed

(d) interference pattern will not form on the screen

40. In the Young’s double slit experiment, separation between the two slits is 0.9 mm and the fringes are observed one metre away. if it produces the second dark fringe at a distance of 1 mm from the central fringe, then wavelength of the monochromatic source of light used is *

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(a) 400 mm

(b) 450 mm

(c) 500 mm

(d) 600 nm

41. In the Young’s double slit experiment, initially equal intensities were coming out of the two slits S1 and S2 . Now if infront of one slit, a glass sheet which absorbs half of the intensity is placed, then *

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(a) the brighter fringes will become comparatively darker

(b) the darker fringes will become comparatively brighter

(c) the central fringe will shift on the side of the glass plate

(d) all of the above

42. The fringe width in Young’s double slit experiment increases when *

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(a) wavelength increases

(b) distance between source and screen decreases

(c) distance between slits increases

(d) the width of the slits increases

43. If in an interference pattern, Imax. represents the intensity maximum value and I min. represents the intensity minimum value, then the fringe visibility is defined a *

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(a) V = Imax./1\lmin.

(b) V = I max. + lmin/ l.max. lmin. - l max. min

(c) V = I max. - lmin/ l.max. lmin. +lmax. min

(d) V = I max. - lmin/ l.max. lmin. +lmax. min

44. What happens to the fringe pattern, when the Young’s double slit experiment is performed in water instead of air *

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(a) Shrinks

b) Disappear

(c) Unchanged

(d) Enlarged

45. In Young’s double slit experiment, illuminated by yellow light, one slit is covered with plane transparent thin glass plate and the other slit by blue filter. Then *

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(a) there will be yellow and blue interference fringes formed on the screen

(b) there will be uniform illumination on the screen

(c) the maximum intensity fringes will be doubly coloured

(d) the minimum intensity fringes will be dark

46. If one of the two slits of a Young’s double slit experiment is painted over so that it transmits half the light intensity of the other, then *

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(a) the fringe system would disappear

(b) the bright fringes will be more bright and dark fringes will be more dark

(c) the dark fringes would be brighter and bright fringes would be darker

(d) bright as well as dark fringes would be darker

47. In the Young’s double slit experiment, the two equally bright slits are coherent, but of phase difference p/3. If the maximum intensity on the screen is Io , the intensity at the point on the screen equidistant from the slits is *

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(a) Io

(b) Io/2

(c) Io/4

(d) 3I/4

48. In Young’s double slit experiment if two slightly different wavelengths are present in the light used then *

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(a) the sharpness of fringes will increase everywhere (compared to the case when monochromatic light is

(b) there will be no fringes at all

(c) the sharpness of fringes will decrease as we move away from central fringe

(d) the central fringe will be white

49. White light may be considered to be a mixture of waves with l ranging between 3000 Å and 7800 Å. Anoil film of thickness 10000 Å is examined normally by the reflected light. If m = 1.4, then the film appears bright for *

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(a) 4308 Å, 5091 Å, 6222 Å

(b) 4000 Å, 5091 Å, 5600 Å

(c) 4667 Å, 6222 Å, 7000 Å

(d) 4000 Å, 4667 Å, 5600 Å, 7000 Å

50. A source emits electromagnetic waves of wavelength 3 m. One beam reaches the observer directly and other after reflection from a water surface, travelling 1.5 m extra distance and with intensity reduced to (1/4) as compared to intensity due to direct beam alone. The resultant intensity will be *

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(a) (1/4) fold

(b) (3/4) fold

(c) (5/4) fold

(d) (9/4) fold

51. Huygens’ wave theory allows us to know *

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(a) the wavelength of the wave

(b) the velocity of the wave

(c) the amplitude of the wave

(d) the propagation of wavefronts

52. In Young’s double slit experiment, the source S and two slits A and B are horizontal with slit A above slit B. The fringes are observed on a vertical screen K. The optical path length from S to B is increased very slightly (by introducing a transparent material of higher refractive index) and optical path length from S to A is not changed. As a result the fringe system on K moves *

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(a) vertically downwards slightly

(b) vertically upwards slightly

(c) horizontally, slightly to the left

(d) horizontally, slightly to the right

53. Sir C.V. Raman received Nobel prize for which of the following phenomenon? *

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(a) Theory of relativity

(b) Law of gravitation

(c) Neutron

(d) Elastic scaterring of light by molecules

54. In Young’s double slit experiment the wavelength of light was changed from 7000 Å to 3500 Å. While doubling the separation between the slits which of the following is not true for this experiment? *

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(a) The width of the fringes changes

(b) The colour of the bright fringes changes

(c) The separation between successive bright fringes changes

(d) The separation between successive dark fringes remains unchanged

55. A thin mica sheet of thickness 2 × 10–6 m and refractive index m = 1.5 is introduced in the path of one of the waves. The wavelength of the wave used is 5000 Å. The central bright maximum will shift *

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(a) 2 fringes upward

(b) 2 fringes downward

(c) 10 fringes upward

(d) none of these

56. The maximum intensity in Young’s double slit experiment is Io . Distance between the slits is d = 5l, where l is the wavelength of monochromatic light used in the experiment. What will be the intensity of light in front of one of the slits on a screen at a distance D = 10d? *

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(a) Io/2

(b) 3Io/4

(c) Io

(d) Io/4

57. If two coherent sources are placed at a distance 3l from each other symmetric to the centre of the circle shown in the figure, then number of fringes shown on the screen placed along the circumference is *

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(a) 16

(b) 12

(c) 8

(d) 4

58. Two waves, whose intensities are 9: 16 are made to interfere. The ratio of maximum and minimum intensities in the interference pattern is *

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(a) 49: 1

(b) 25: 7

(c) 10: 9

(d) 4: 3

59. Two identical coherent sources are placed on a diameter of a circle of radius R at separation x (<< R ) symmetrically about the centre of the circle. The sources emit identical wavelength l each. The number of points on the circle with maximum intensity is (x = 5l *

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(a) 20

(b) 22

(c) 24

(d) 26

60. Microwaves from a transmitter are directed normally towards a plane reflector. A detector moves along the normal to the reflector. Between positions of 14 successive maxima the detector travels a distance of 0.14 m. The frequency of transmitter is (c = 3 × 108 m/s) *

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(a) 1.5 × 1010 Hz

(b) 1010 Hz

(c) 3 × 1010 Hz

(d) 6 × 1010 Hz

61. In Young’s double slit experiment, the type of diffraction is *

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a) Fresnel

(b) Fraunhofer

(c) both (a) and (b)

(d) none of these

62. The phase difference between two wave trains giving rise to a dark fringe in Young’s double slit interference experiment in (n integer) *

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a) 2pn + p/4

(b) 2pn + p

(c) 2pn + p/2

(d) zero

63. In Young’s double slit interference pattern the fringe width *

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(a) can be changed only by changing the wavelength of incident light

(b) cab be changed only by changing the separation between the two slit

(c) can be changed either by changing the wavelength or by changing the separation between the two slits

(d) is a universal constant, hence cannot be changed

64. When petrol drops from a vehicle fall over rain water on the road, colours are seen because of *

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(a) dispersion of light

(b) scattering of light

(c) interference of light

(d) absorption of light

65. What is the minimum thickness of a soap bubble needed for constructive interference in reflected light if the light incident on the film is 900 nm? Assume the refractive index for the film is m = 1.5 *

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(a) 100 nm

(b) 150 nm

(c) 200 nm

(d) 250 nm

66. A Young’s double slit experiment uses a monochromatic source. The shape of the interference fringes formed on the screen is a *

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(a) straight line

(b) parabola

(c) hyperbola

(d) circle

67. In Young’s double slit experiment, a third slit is made in between the double slits, Then *

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(a) intensity of fringes totally disappears

(b) only bright light is observed on the screen

(c) fringes of unequal width are formed

(d) contrast between bright and dark fringes is reduced

68. If white light is used in a biprism experiment then *

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(a) fringe pattern disappears

(b) all fringes will be coloured

(c) central fringe will be white while others will be coloured

(d) increase or decrease depending upon the prism angle

69. In a biprism experiment, if the biprism is moved towards the light source a little, then the fringe width will *

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(a) increase

(b) decrease

(c) not change

(d) increase or decrease depending upon the prism angle

70. In a Fresnel biprism experiment, the two positions of lens give separation between the slits as 16 cm and 9 cm respectively. What is the actual distance of separation? *

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(a) 12.5 cm

(b) 12.0 cm

(c) 13 cm

(d) 14 cm

71. The phenomenon of diffraction can be exhibited by *

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(a) polarised waves only

(b) unpolarised waves only

(c) longitudinal waves only

(d) all, polarised or unpolarised, longitudinal or transverse wave

72. The main difference in the phenomenon of interference and diffraction is that *

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(a) diffraction is due to interaction of light from the same wavefront whereas interference is the interaction of waves from two isolated sources

(b) diffraction is due to interaction of light from same wavefront, whereas the interference is the interaction of two waves derived from the same source

(c) diffraction is due to interaction of waves derived from the same source, whereas the interference is

(d) diffraction is caused by the reflected waves from a source whereas interference is caused due to refraction of waves from a sourc

73. The phenomenon of diffraction can be exhibited by *

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(a) infrared waves

(b) microwaves

(c) X-rays

(d) all of these

74. Diffraction effects are easily observable for *

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(a) microwaves

(b) sound waves

(c) radio waves

(d) all of these

75. In Fresnel’s class of diffraction, the *

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(a) obstacle-screen distance is small

(b) the diffracted wavefront is considered as spherical

(c) no convex lens is used to focus the diffraction fringes on the screen

(d) all of the above

76. A diffraction pattern is obtained using a beam of red light. What happens if the red light is replaced by blue light? *

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(a) No change

(b) Diffraction bands become narrower and crowded together

(c) Bands become broader and farther apart

(d) Bands disappear

77. nth bright fringe if red light (l1 = 7500 Å) coincides with (n + 1)th bright fringe of green light (l2 = 6000 Å.) The value of n =? *

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(a) 4

(b) 5

(c) 3

(d) 2

78. A parallel beam of fast moving electrons is incident normally on a narrow slit. A screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statement is correct? *

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(a) Diffraction pattern is not observed on the screen in the case of electron.

(b) The angular width of the central maximum of the diffraction pattern will increase.

(c) The angular width of the central maximum will decrease

(d) The angular width of the central maximum will remains the same.

79. A slit of width a is illuminated with a monochromatic light of wavelength l from a distant source and the diffraction pattern is observed on a screen placed at a distance D from the slit. To increase the width of the central maximum one should *

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(a) decrease D

(b) decrease a

(c) decrease l

(d) the width cannot be changed

80. Polarisation of light proves the *

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(a) corpuscular nature of light

(b) quantum nature of light

(c) transverse wave nature of light

(d) longitudinal wave nature of light

81. The fact that light is transverse wave phenomenon derives its evidential support from the observation that *

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(a) light is a wave motion

(b) light is characterised by interference

(c) light shows polarising effects

(d) light can be diffracted

82. If light is polarised by reflection, then the angle between reflected and refracted light is *

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(a) p

(b) p/2

(c) 2p

(d) p/4

83. One of the devices to produce plane polarised light is *

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(a) nicol prism

(b) a crystal

(c) a biprism

(d) a half wave plate

84. A ray of unpolarised light is incident on a glass plate at the polarising angle 57º. Then *

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(a) the reflected ray and the transmitted ray both will be completely polarised

(b) the reflected ray will be completely polarised and the transmitted ray will be partially polarised

(c) the reflected ray will be partially polarised and the transmitted ray will be completely polarised

(d) the reflected and transmitted both rays will be partially polarised

85. Polaroid glass is used in sun glasses because *

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a) it reduces the light intensity to half on account of polarisation

(b) it is fashionable

(c) it has good colour

(d) it is cheaper

86. Waves that cannot be polarised are *

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(a) light waves

b) electromagnetic waves

(c) transverse waves

(d) longitudinal waves

87. The phenomenon of rotation of plane polarised light is called *

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(a) double refraction

b) kerr effect

(c) dichroism

d) optical activity

88. An optically active compound *

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(a) rotates the plane polarised light

(b) changes the direction of polarised light

(c) do not allow lane polarised light to pass through

(d) none of the above

89. In case of linearly polarised light, the magnitude of the electric field vector *

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(a) does not change with time

(b) varies periodically with time

(c) increases and decreases linearly with time

(d) is parallel to the direction of propagation

90. A Nicol prism is based on the principle of *

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(a) refraction

(b) scattering

(c) dichroism

(d) double refraction

91. What does not change on polarization of light? *

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(a) Intensity

(b) Phase

(c) Frequency

(d) Wavelength

92. A calcite crystal is placed over a dot on a piece of paper and rotated; On seeing through the calcite, one will see *

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(a) one dot

(b) two stationary dots

(c) two rotating dots

(d) one dot rotating about the other

93. A polaroid is placed at 45º to an incoming light of intensity Io . Now the intensity of light passing through the polaroid after polarisation would b *

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(a) Io

(b) Io/2

(c) Io/4

(d) zero

94. Which of the following cannot be explained on the basis of wave nature of light? i) Polarization (ii) Optical activity (iii) Photoelectric effect (iv) Compton effect *

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(a) (iii) and (iv)

(b) (ii) and (iii)

(c) (i) and (iii)

(d) (ii) and (iv)

95. What happens inside optical fibre? *

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a) Diffraction

(b) Polarisation

(c) Interference

(d) Total Internal reflection

96. The phenomenon of polarisation of electromagnetic waves proves that the electromagnetic waves are *

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(a) transverse

(b) mechanical

(c) longitudinal

(d) neither longitudinal nor transverse

97. Which of the following as a dichroic crystal? *

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(a) Quartz

(b) Tourmaline

(c) Mica

(d) Selenite

98. When the light is incident at the polarizing angle on the transparent medium, then the completely polarized light is *

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a) refracted light

(b) reflected light

(c) refracted and reflected light

(d) neither reflected nor refracted light

99. The dispersive powers of the materials of the two lenses are in the ratio 3 : 4. If the achromatic combination of these two lenses is of focal length 60 cm, then the focal lengths of the component lenses ar *

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(a) + 15 cm and – 20 cm

(b) – 15 cm and – 20 cm

(c) + 20 cm and – 25 cm

(d) –20 cm and + 25 cm

100. The angle of incidence of light is equal to Brewster’s angle, then (1) reflected ray is perpendicular to refracted ray (2) reflected ray is parallel to refracted ray (3) reflected light is polarized having its electric vector in the plane of incidence (4) refracted light is polarized *

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(a) (1) and (4) are true

(b) (1) and (2) are true

(c) (1) and (3) are true

(d) (2) and (4) are true

1. The fact that light is a transverse wave in nature derives its evidence by the support from the observation that *

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(a) light waves undergo reflection

(b) light can be diffracted

(c) light travels in waves

(d) light shows polarising effects

2. Light from a denser medium I goes to a rarer medium II. When angle of incidence is q, the reflected and refracted rays are perpendicular to each other? *

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(a) sin–1(cosq)

(b) sin–1(cotq)

(c) sin–1(tanq)

(d) sin–1(1)

8. What causes change in the colours of the soap or oil films for the given beam of light? *

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(a) Angle of incidence

(b) angle of reflection

(c) thickness of film

(d) none of the above

9. Refractive index of a material is equal to tangent of polarising angle. It is called *

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(a) Brewster’s law

(b) Lambert’s law

(c) Malus law

(d) Bragg’s law

10. Sir C.V. Raman was awarded Nobel prize for his work concerned with which of the following phenomena of radiation? *

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(a) Scattering

(b) Diffraction

(c) Interference

(d) Polarisation

11. Which one of the following statements is true? *

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(a) Both light and sound waves in air are transverse

(b) The sound waves in air are longitudinal, while the light waves are transverse

(c) Both light and sound waves in air are longitudinal

(d) Both light and sound waves can travel in vacuum

12. The frequency of a light wave in a material is 2 × 1014 Hz and wavelength is 5000 Å. The refractive index of material will be *

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(a) 1.50

(b) 3.00

(c) 1.33

(d) 1.40

1. Consider a light beam incident from air to a glass slab at Brewster’s angle as shown in below figure. A polaroid is placed in the path of the emergent ray at point P and rotated about an axis passing through the centre and perpendicular to the plane of the polaroid. *

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(a) For a particular orientation there shall be darkness as observed through the polaroid.

(b) The intensity of light as seen through the Polaroid shall be independent of the rotation.

(c) The intensity of light as seen through the Polaroid shall go through a minimum but not zero for two

(d) The intensity of light as seen through the Polaroid shall go through a minimum for four orientations of

2. Consider sunlight incident on a slit of width 104 A. The image seen through the slit shall *

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(a) be a fine sharp slit white in colour at the center.

(b) a bright slit white at the center diffusing to zero intensities at the edges.

(c) a bright slit white at the center diffusing to regions of different colours.

(d) only be a diffused slit white in colour

4. In a Young’s double slit experiment, the source is white light. One of the holes is covered by a red filter and another by a blue filter. In this case *

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(a) there shall be alternate interference patterns of red and blue.

(b) there shall be an interference pattern for red distinct from that for blue.

(c) there shall be no interference fringes.

(d) there shall be an interference pattern for red mixing with one for blue.

5. Figure below shows a standard two slit arrangement with slits S1 , S2 , P1 , P2 are the two minima points on either side of P. At P2 on the screen, there is a hole and behind P2 is a second 2- slit arrangement with slits S3 , S4 and a second screen behind them. *

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(a) There would be no interface pattern on the second screen but it would be lighted.

(b) The second screen would be totally dark.

(c) There would be a single bright point on the second screen.

(d) There would be a regular two slit pattern on the second screen

1. At what angle of incidence will the light reflected from glass (m = 1.5) be completely polarized *

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(a) 56.3º

(b) 40.3º

(c) 72.8º

(d) 51.6º

2. When light rays enter in a glass slab, their wavelength *

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(a) remains unchanged

(b) decreases

(c) increases

(d) either (a) or (b)

3. A beam of light in air enters into the water. Which of the following characteristics of light will not change? *

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(a) colour

(b) velocity

(c) amplitude

(d) frequency

4. In an elliptically polarised light, the amplitude of the vibrations *

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(a) remains constant

(b) changes in direction only

(c) changes in magnitude only

(d) both (b) and (c)

5. In Young’s experiment, the monochromatic light is used to illuminate two slits A and B as shown. Interference fringes are observed on a screen placed in front of the slits. Now if a thin glass plate is placed normally in the path of beam coming from the slit A, then *

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(a) fringe width will decrease

(b) fringes will disappear

(c) fringe width will increase

(d) there will be no change in fringe width

6. Relation between critical angle of water and the glass is *

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(a) Cw = Cg= 0

(b) Cw = Cg

(c) Cw > Cg

(d) Cw < Cg

7. Interference occurs in which of the following waves? *

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(a) transverse

(b) longitudinal

(c) electromagnetic

(d) all of these

8. When a of light enters a glass slab, then *

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(a) its frequency and velocity changes

(b) only frequency changes

(c) its frequency and wavelength changes

(d) its frequency does not change

9. Ratio of intensities of two waves is 9: 1. If these two are superimposed, what is the ratio of maximum and minimum intensities? *

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(a) 9: 1

(b) 3: 1

(c) 4: 1

(d) 5: 3

Option 5

10. A light of intensity I o passes through a material of thickness d. The resultant intensity *

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(a) I = Io e–dl

(b) I = Io(1 – e–dl)

(c) I = Io e–d/l

(d) I = Io(1 –e–d/l

11. A light wave moves from air to glass with frequency n and wavelength l. Then *

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(a) n changes

(b) n does not change, l change

(c) l does not change

(d) n and l changes

12. Two coherent monochromatic light beams of amplitude 3 and 5 units are superposed. The maximum and minimum possible intensities in the resulting beams are in the ratio *

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(a) 4: 2

(b) 16: 1

(c) 8: 2

(d) 4: 2

13. If red light is replaced by white light then width of diffraction pattern w *

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(a) increases

(b) decreases

(c) a central white band is obtained

(d) no effect.

14. Light propagates rectilinearly because of its *

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(a) frequency

(b) velocity

(c) wavelength

(d) wave nature

15. The Cauchy’s dispersion formula is *

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(a) n = A + Bl–2 +Cl–4

(b) n = A + Bl–2 +Cl4

(c) n = A + +Cl–4

(d) n = A + +Cl4

16. Golden view of sea shell is due to *

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(a) diffraction

(b) polarisation

(c) dispersion

(d) reflection

17. What is the path difference for destructive interference? *

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(a) nl

(b) (n+l)/2 l

(c) n(l + 1)

(d) ( ) 2n +1)/2 l

18. A laer beam is used for carrying out surgery because it

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(a) is highly monochromatic

(b) is highly coherent

(c) is highly directional

(d) can be sharply focussed

Clear selection

19. When a beam of light is used to determine the position of an object, the maximum accuracy is achieved if the light is *

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(a) polarised

(b) of longer wavelength

(c) of shorter wavelength

(d) of high intensity

20. A double slit experiment is performed with light of wavelength 500 nm. A thin film of thickness 2 mm and refractive index 1.5 is introduced in the path of the upper beam. The location of the central maximum will *

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(a) remain unshifted

(b) shift downward by nearly two fringes

(c) shift upward by nearly two fringes

(d) shift downward by 10 fringes

21. Sodium lamps are used in foggy conditions because *

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(a) yellow light is scattered less by the fog particles

(b) yellow light is scattered more by the fog particles

(c) yellow light is unaffected during its passage through the fog

(d) wavelength of yellow light is the mean of the visible part of the spectrum

22. A monochromatic beam of light is used for the formation of fringes on the screen by illuminating the two slits in the Young’s double slit interference experiment. When a thin film of mica is interposed in the path of one of the interfering beams then *

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(a) the fringe width increases

(b) the fringe width decreases

(c) the fringe width remains the same but the pattern shifts

(d) the fringe pattern disappears

23. When a compact disc is illuminated by a source of white light, coloured lines are observed. This is due to *

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(a) dispersion

(b) diffraction

(c) interference

(d) refraction

24. When exposed to sunlight, thin films of oil on water often exhibit brilliant colours due to the phenomenon of *

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(a) interference

(b) diffraction

(c) dispersion

(d) polarisation

25. In case of linearly polarised light, the magnitude of the electric field vector *

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(a) does not change with time

(b) varies periodically with time

(c) increases and decreases linearly with time

(d) is parallel to the direction of propagation

26. A stone thrown into still water, creates a circular wave pattern moving radially outwards. If r is the distance measured from the centre of the pattern, the amplitude of the wave varies as *

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(a) r–1/2

(b) r–1

(c) r–2

(d) r–3/2

27. Flash light equipped with a new set of batteries, produces bright white light. As the batteries, wear o *

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(a) the light intensity gets reduced with no change in its colour

(b) light colour changes first to yellow and then red with no change in intensity

(c) it stops working suddenly while giving white light

(d) colour changes to red and also intensity gets reduced

28. A point source is kept at a distance of 1000 m has an illumination I. To change the illumination to 16i the new distance should become *

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(a) 250 m

(b) 500 m

(c) 750 m

(d) 800 m

29. In Young’s double slit experiment, the distance between two slits is made three times then the fringe width will become *

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(a) 9 times

(b) 1/9 times

(c) 3 times

(d) 1/3 times

30. When white light passes through a prism, the deviation is maximum for *

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(a) violet light

(b) green light

(c) red light

(d) yellow light

31. Light is incident normally on a diffraction grating through which the first diffraction is seen at 32º. In this case the second order diffraction will be *

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(a) at 80º

(b) at 64º

(c) at 48º

(d) there is no second order diffraction

32. Which out of following, cannot produce two coherent sources? *

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(a) Lloyd’s mirror

(b) Fresnel biprism

(c) Young’s double slit

(d) Prism

33. The intensity of gamma radiation from a given source is l. On passing through 36 mm of lead, it is reduced to l/8. The thickness of lead which will reduce the intensity to l/2 will be *

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(a) 18 mm

(b) 12 mm

(c) 6 mm

(d) 9 mm

34. In an interference, the intensity of two interfering waves are I and 4I respectively. They produce intensity at two points A and B with phase angle of p/2 and p respectively. Then difference in between them is *

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(a) I

(b) 2I

(c) 4I

(d) 5I

35. In a single slit diffraction with l = 500 nm and a lens of diameter 0.1 mm then width of central maxima, obtain on screen at a distance of 1 m will be *

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(a) 5 mm

(b) 1 mm

(c) 10 mm

(d) 2.5 mm

36. In Young’s double slit experiment, fringe order is represented by m, then fringe width is *

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(a) Independent of m

(b) Directly proportional to m

(c) Directly proportional to (2m + 1)

(d) Inversely proportional to (2m + 1)

37. Polaroid glass is used in sun glasses because *

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(a) it reduces the light intensity to half on account of polarisation

(b) it is fashionable

(c) it has good colour

(d) it is cheaper

38. In a Young’s double slit experiment the spacing between the slits is 0.3 mm and the screen is kept at a distance of 1.5 m. The second bright fringe is found 6 mm from the central fringe. The wavelength of the light used in the experiment is *

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(a) 625 nm

(b) 600 nm

(c) 550 nm

(d) 500 nm

39. The frequency of a light wave in a material is 2 × 1014 Hz and wavelength is 5000 Å. The refractive index of material will be *

1 point

(a) 1.50

(b) 3.00

(c) 1.33

(d) 1.40

40 For Bragg’s diffraction by a crystal to occur, then the X-ray of wavelength l and interatomic distance d must be *

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(a) l is greater than 2d

(b) l equals 2d

(c) l is smaller than or equal to 2d

(d) l is smaller than 2d

41 What changes occur, if the monochromatic light used in Young’s double slit experiment is replaced by white light? *

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(a) Only the central fringe is white and all other fringes are observed coloured

(b) No fringes are observed

(c) All the bright fringes become white

(d) All the bright fringes are coloured between violet and red

44. Diffraction pattern of a single slit consists of a central bright band which is *

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(a) wide, and is flanked by alternate dark and bright bands of decreasing intensity

(b) narrow, and is flanked by alternate dark and bright bands of equal intensity

(c) wide, and is flanked by alternate-dark and bright bands of equal intensity

(d) narrow, and is flanked by alternate-dark and bright bands of decreasing intensity