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Question Bank No: 2

1. In Young's experiment for interference of light with two slits, reinforcement takes place when sin $θ$ = $\frac{d}{λ m},$ d is

a)		distance from slits to the screen
b)		distance between dark and bright fringes
c)		distance between slits
d)		width of mth fringe

2. A thin oil layer floats on water. A ray of light making an angle of incidence of $40^{o}$ shines on oil layer. the angle of refraction of light ray with water surface is
( $μ_{oil}$ =1.45, $μ_{water}$ =1.33)

a)		${36.1}^{o}$
b)		${44.5}^{o}$
c)		${26.8}^{o}$
d)		${28.9}^{o}$

3. If ratio of amplitude of two wave is 4 : 3, then ration of maximum and minimum intensity is

a)		16 : 18
b)		18 : 16
c)		49 : 1
d)		94 : 1

4. When light wave suffers reflection at the interface from air to glass, the change in phase of the reflected light is equal to

a)		0
b)		$π / 2$
c)		$π$
d)		2 $π$

5. The interfering fringes formed by a thin of film on water are seen in yellow light of sodium lamp. We find the fringes are

a)		coloured
b)		black and white
c)		yellow and black
d)		coloured without yellow

6. The limit of resolution of eye is approximately

a)		$1^{o}$ angle
b)		$1^{'}$ angle
c)		1 mm
d)		1 cm

7. A ray of light consisting of two wavelengths 4000 Angstrom and 5000 Angstrom falls from air on a quarts surface. The angle of incidence is $30^{o}$ , and refractive indices for the wavelengths are respectively 1.47 and 1.46. The angle between the two refracted beams will be

a)		$0^{o}$
b)		$45^{o}$
c)		$90^{o}$
d)		${0.14}^{o}$

8. In Young's experiment, the distance between two slits is d/3 and the distance between the screen and the slits is 3D. The number of fringes in 1/3 m on the screen, formed by mono chromatic light of wavelength 3 $λ$ , will be

a)		$\frac{d}{9 D λ}$
b)		$\frac{d}{27 D λ}$
c)		$\frac{d}{81 D λ}$
d)		$\frac{d}{D λ}$

9. A ray of light is incident on the surface of a glass plate at an angle of incidence equal to Brewster's angle $φ$ . If $μ$ represents the refractive index of glass with respect to air, then angle between the reflected and refracted rays is

a)		$90^{o} + φ$
b)		$\sin^{- 1} (μ \cos φ)$
c)		$90^{o}$
d)		$0^{o} - \sin^{- 1} (\frac{\sin φ}{μ})$

10. The Young's double slit experiment is performed with blue and with green light of wavelengths 4360A and 5460A respectively. If x is the distance of 4th maxima from the central one, then

a)		x (blue) = x (green)
b)		x (blue) > x (green)
c)		x (blue) < x (green)
d)		x (blue) / x (green) = 5460/4360

11. The axis of two Nicol prisms are parallel to one another. One of the two Nicols is rotated through an angle of $60^{o}$ . The ration of the intensity of transmitted light before and after rotation is

a)		1 : 2
b)		2 : 1
c)		4 : 1
d)		1 : 4

12. The limit of resolution of an optical instrument arises an account of

a)		interference
b)		diffraction
c)		polarization
d)		none of these

13. $V_{0}$ and $V_{E}$ represent the velocities, $μ_{0}$ and $μ_{E}$ the refractive indices of ordinary and extraordinary rays for a doubly refracting crystal. Then

a)		$V_{0} \leq V_{E}$ , $μ_{0} \geq μ_{E}$ , if the crystal is calcite
b)		$V_{0} \geq V_{E}$ , $μ_{0} \geq μ_{E}$ , if the crystal is quartz
c)		$V_{0} \geq V_{E}$ , $μ_{0} \leq μ_{E}$ , if the crystal is calcite
d)		$V_{0} \leq V_{E}$ , $μ_{0} \leq μ_{E}$ , if the crystal is quartz

14. Two sources of light of wavelengths 2500 A and 3500 A are used in Young's double slit expt. simultaneously. Which orders of fringes of two wavelength patterns coincide.

a)		3rd order of 1st source and 5th of the 2nd
b)		7th order of 1st and 5th order of 2nd
c)		5th order of 1st and 3rd order of 2nd
d)		5th order of 1st and 7th order of 2nd

15. A red piece of paper when illuminated by green light appears

a)		Blue
b)		Yellow
c)		Green
d)		Black

16. Oil floating on water looks coloured due to the interference of light. The approximate thickness of oil for such effect to be visible is

a)		100A
b)		1000A
c)		1mm
d)		1cm

17. In a biprism experiment, 5th dark fringes obtained at a point . If a thin transparent film is placed in the path of one of waves, then 7th bright fringe is obtained at the same point. The thickness of the film in terms of wavelength $λ$ and refractive index $μ$ will be

a)		$\frac{1.5 λ}{(μ - 1)}$
b)		1.5 ( $μ - 1) λ$
c)		2.5 ( $μ - 1) λ$
d)		$\frac{2.5 λ}{(μ - 1)}$

18. A single slit of width d is placed in the path of beam of wavelength $λ$ . The angular width of the principal maximum obtained is

a)		d/ $λ$
b)		$\pm λ / d$
c)		2 $λ / d$
d)		2d/ $λ$

19. Two beams of light having intensities I and and 4I interface to produce a fringe pattern on a screen. The phase difference between the beams is $π / 2$ at point a and $π$ at point B. Then the difference between the resultant intensities at A and B is

a)		2I
b)		4I
c)		5I
d)		7I

20. The fringe width $β$ of the fringes produced in Young's double slit experiment is

a)		$β = \frac{λ D}{d}$
b)		$β = D \frac{d}{λ}$
c)		$β = \frac{λ d}{D}$
d)		$β = λ d^{2} / D^{2}$

21. In youngs' double slit experiment carried out with light of wavelength $λ$ =5000A, the distanc between the slits is 0.2mm and the screen is at 200 cm for the slits. The central maximum is at x=0. The third maximum (taking the central maximum as xeroth maximum) will be x equal to

a)		1.67 cm
b)		1.5cm
c)		0.5 cm
d)		5.0 cm

22. Newton's corpuscular theory states that velocity of light is rarer medium as compared to that in a denser medium is

a)		less
b)		more
c)		sometimes less, sometimes more
d)		much less

23. In two seperate set ups of Young's double slit experience using light of same wavelength, fringes of equal width are observed. If ratio of slit seperation in the two is 2:3, the ratio of the distance between source and screen placed in the two set ups is

a)		2:3
b)		3:2
c)		4:9
d)		9:4

24. Which out of the following , cannot produce two coherent sources?

a)		Lloyd's Mirror
b)		Fresnel's biprism
c)		Young's double slit
d)		Prism

25. Light appears to travel in a 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

26. Two coherent waves are represented by $y_{1}$ = $a_{2}$ sin $ω t$ . The resultant intensity due to interference will be

a)		( $a_{1}$ $+ a_{2}$ )
b)		( $a_{1} - a_{2})$
c)		( $a_{2}^{1} + a_{2}^{2}$ )
d)		( $a_{2}^{1} - a_{2}^{2}$ )

27. If light is completely polarised by reflection at a plane refracting surface then the angle between reflected and refracted light is

a)		$π$
b)		$\frac{π}{2}$
c)		$\frac{π}{4}$
d)		$\frac{π}{6}$

28. To observe diffraction effects, the size of the obstacle

a)		should be of the same order as the wave length of light used
b)		should be much larger than the wave length
c)		should exactly be $\frac{λ}{2}$
d)		none of the above

29. In interference there is redistribution of

a)		amplitude
b)		frequency
c)		phase
d)		energy

30. Choose the correct statement

a)		Brewsters angle is independent of the wavelength
b)		Brewsters angle is independent of the material of the reflecting surface
c)		Brewsters angle depends on wave length but not on the nature of the reflecting surface
d)		Brewsters angle is different for different wave length

31. The angle of polarisation of glass $58^{\circ}$ and that for water $53^{\circ}$ . The angle of polarisation for glass from water is

a)		$\frac{1}{\tan 58 \times \tan^{- 1} 53}$
b)		${\tan 53}^{\circ} \times {\tan 58}^{\circ}$
c)		$\tan^{- 1} [\frac{\tan 58}{\tan 53}]$
d)		$\tan^{- 1} [\frac{\tan 53}{\tan 58}]$

32. A ray of light from air is incident on the surface of glass at polarising angle. It suffers a deviation of $22^{\circ}$ on entering glass. The angle of polarisation is

a)		$22^{\circ}$
b)		$56^{\circ}$
c)		$68^{\circ}$
d)		$34^{\circ}$

33. Which of the following phenomena is not common to sound and light waves

a)		interference
b)		diffraction
c)		polarisation
d)		reflection

34. In a single slit experiment, the width of the slit is doubled. Which one of the following statement is correct?

a)		the intensity and width of the central maximum are un affected
b)		the intensity remains the same and the angular width becomes half
c)		the intensity and angular width are both doubled
d)		the intensity increases by a factor 4 and the angular width decreases by a factor 1/2.

35. The first diffraction maximum due to a single slit diffraction is at $θ = 30^{\circ}$ for light of wave length $λ$ = 500 nm. The width of the slit is

a)		500nm
b)		10000nm
c)		250nm
d)		125nm

36. Diffraction of sound is very easy to observe in day today life. This is not so with light . This is because

a)		$λ s > λ l$
b)		$λ s < λ l$
c)		$λ s = λ l$
d)		none of the above

37. A mixture of yellow light of wave length 580nm and blue light of wave length 450 nm is incident normally on an air film of thicken ${2.9 \times 10}^{- 4}$ nm. The color of the reflected light is

a)		red
b)		blue
c)		violet
d)		yellow

38. Two waves originating from sources $S_{1}$ and $S_{2}$ having zero phase difference and common wave length $λ$ will show destructive interference at a point P if $S_{2} P - S_{1} P$ is

a)		5 $λ$
b)		$\frac{3 λ}{4}$
c)		2 $λ$
d)		$\frac{11 λ}{2}$

39. Two light rays having the same wave length in vaccum are in phase initially. Then the first ray travels a path of length $L_{1}$ through a medium of refractive index $n_{2}$ . The two waves are then combined to observe interference effects. The phase difference between the two when they interference is

a)		$\frac{2 π}{λ} (L_{1} - L_{2})$
b)		$\frac{2 π}{λ} [n_{1} L_{1} - n_{2} L_{2}]$
c)		$\frac{2 π}{λ} [n_{1} L_{2} - n_{2} L_{2}]$
d)		$\frac{2 π}{λ} [\frac{4}{n_{1}} - \frac{L_{2}}{n_{2}}]$

40. color in a thin film results from

a)		dispersion of light
b)		interference of light
c)		absorption of light
d)		scattering of light

41. Laser light (630nm) incident on a pair of slits produces an interference pattern in which the bright fingers are seperated by 8.3 mm a second light produces interference pattern in which bright fingers are seperated by 7.6mm. The wavelength of the second light is about

a)		58nm
b)		580 nm
c)		630 nm
d)		580 $μ$ m

42. In air an interference pattern produced by two identical slits the intensity at the central maximum is I. The intensity at the same spot when either of the two slits is closed is $I_{0}$ . This means that

a)		I = $I_{0}$
b)		I = $2 I_{0}$
c)		I = ${3 I}_{0}$
d)		I = ${4 I}_{0}$

43. Polarisation of light proves

a)		corpuscular nature of light
b)		quantum nature of light
c)		transverse nature of light
d)		longitudinal nature of light

44. Two coherent sources of intersities I and 4I are superposed. The maximum and minimum possible intensities in the resultant beam is

a)		5I and I
b)		9I and I
c)		5I and 3I
d)		9I and 8I

45. In Young double slit experiment, the seperation between the slits is halved and the distance between the slit and the screen doubled. The fringe width is

a)		unchanged
b)		doubled
c)		halved
d)		quadrupled

46. In young double slit experiment, the ratio of the maximum to minimum intensities in the fringe system is 9 : 1. The ratio of the amplitudes of the coherent sources is

a)		9 : 1
b)		3 : 1
c)		2 : 1
d)		1 : 1

47. Which of the following does not support the wave nature of light?

a)		interference
b)		diffraction
c)		polarisation
d)		photoelectric effect

48. The linear distance between successive points that have same phase on any wave is called

a)		amplitude
b)		frequency
c)		wavelength
d)		period

49. When a ray of light enters a glass slab from air

a)		its wavelength decreases
b)		its wavelength increases
c)		its frequency increases
d)		none of the above

50. Two sources are said to be coherent if

a)		they produce waves of the same wavelength
b)		they produce waves of the same amplitude
c)		they produce waves of the same wave length having constant initial phase difference
d)		they are of the same amplitude and same frequency