Untitled Document

Question Bank No: 1

1. Stars emits light of 5500 $A^{0}$ wave length. It appears blue to an observer on earth. It means

a)		star is moving away from earth
b)		star is stationary
c)		star is moving towards earth
d)		none of the above

2. A ray of unpolarised light is incident on the surface of a glass plate of $μ$ = 1.54 at the polarising angle if 1.54 = tan $57^{0}$ then angle of refraction is

a)		$57^{0}$
b)		$43^{0}$
c)		$33^{0}$
d)		$90^{0}$

3. If the light is polarised by reflection, Then the angle between reflected and refracted light is

a)		$180^{0}$
b)		$90^{0}$
c)		$45^{0}$
d)		$36^{0}$

4. The fraunhofer diffraction pattern of a single slit is formed in the focal plane of lens of focal length 1m. The width of the slit is 0.3 mn. If third minimum is formed at a distance of 5mm from central maximum.Then the wave length of light will be

a)		5000 $A^{0}$
b)		2500 $A^{0}$
c)		7500 $A^{0}$
d)		8500 $A^{0}$

5. The limit of resolution of eye approximately

a)		$1^{0}$ angle
b)		$1^{'}$ angle
c)		1mm
d)		1cm

6. Plane microwaves are incident on a long slit having a width of 5cm. The wavelength of the microwaves if the first minimum is formed at $30^{0}$ is

a)		2.5 cm
b)		5 cm
c)		25 cm
d)		5 mm

7. Let the two interfering beams have intensities 9:4. The intensity ratio in the interference pattern would be

a)		25:1
b)		13:5
c)		5:1
d)		1:25

8. With a monoclromatic light,the fringe width using a glass biprism set up in air is 2mm. Given a $μ_{g} = 3 / 2 a μ_{ω} = 4 / 3.$ The whole set up immersed in water the new fringe width is

a)		2mm
b)		6mm
c)		6/4mm
d)		8/3 mm

9. The velocity of light in diamond ( $V_{d}$ ) and in water $V_{w}$ is such that

a)		$V_{ω} > V_{g} > V_{d}$
b)		$V_{d} > V_{g} > V_{ω}$
c)		$V_{d} > V_{ω} {> V}_{g}$
d)		$V_{ω} > V_{d} > V_{g}$

10. A wire of thickness 0.8 mm is placed between two glass plates making a wedge .The number of fringes visible is 1600.Find wave length used.

a)		10 nm
b)		100 nm
c)		1000 nm
d)		2000 nm

11. Path difference between two wave frounts emitted by coherent sources of wave length 5460 $A^{0}$ is 2.1 micron. The phase difference between the wave frounts at that point is

a)		7.692
b)		7.692 $π$
c)		$\frac{7.692}{π}$
d)		$\frac{7.692}{3 π}$

12. A very thin filim in reflected white light appears

a)		coloured
b)		white
c)		black
d)		red

13. If the distance between slits of Young's lamp im Young's double slit experiment is reduced to half, then the fringe width will become

a)		half
b)		two times
c)		four times
d)		constant

14. Which of the following statement is correct about biological importance of ozone layer?

a)		It stops ultraviolet rays
b)		It reflects radiowaves
c)		It reduces green house effect
d)		It controls $O_{2} / H_{2}$ ratio in atmosphere

15. A slit of width 12 $\times 10^{- 7}$ m is illuminated by light of wavelength 6000A. The angular width of the central maximum is approximately

a)		$30^{o}$
b)		$60^{o}$
c)		$90^{o}$
d)		$0^{o}$

16. The ratio of intensities of consecutive maxima in the diffraction pattern due to single slit is

a)		1:4:9
b)		1:2:3
c)		1: $\frac{4}{9 π^{2}} : \frac{4}{25 π^{2}}$
d)		1: $\frac{4}{π^{2}} : \frac{9}{π^{2}}$

17. In Young's experiment, the wavelength of red light is 7.8 $\times 10^{- 7}$ m and that of the blue light is 5.2 $\times 10^{- 7}$ . The value of n for which (n+1)the blue bright band coincides with the red bright band is

a)		4
b)		3
c)		2
d)		1

18. Monochromatic light of wavelength 5 $\times 10^{- 7}$ m illuminates a pair of narrow slits 1mm apart. The separation of bright lines in the interference pattern formed on a screen 2 metres away is

a)		0.1mm
b)		0.25mm
c)		0.4mm
d)		1.0mm

19. Four different indipendent waves are represented by
(i) $y_{1} = a_{1} \sin ω t$
(ii) $y_{2} = a_{2} \sin 2 ω t$
(iii) $y_{3} = a_{3} \cos ω t$
(iv) $y_{4} = a_{4} \sin (ω t + π / 3)$
with which of two waves interference is possible?

a)		In (i) and (iii)
b)		In (i) and (iv)
c)		In (iii) and (iv)
d)		Not possible with any combination

20. Two slits seperated by a distance of 1mm are illuminated with red light of wavelength 6.5 $\times 10^{- 7}$ metre. The interference fringes are observed on a scree placed one metre from the slits. The distance between the third dark fringe and fifth bright fringe on the same side of centre is equal to

a)		0.65mm
b)		1.63mm
c)		3.25mm
d)		4.8mm

21. Light is incident normally on a diffraction grating through which the first order diffraction is seen at $32^{o}$ . The second order diffraction will be seen at

a)		$48^{o}$
b)		$64^{o}$
c)		$80^{o}$
d)		there is no second order diffraction in this case

22. When a thin film of thickness t is placed in the path of light wave emerging out of source $S_{1}$ then increase in the length of optical path will be

a)		( $μ - 1$ )t
b)		( $μ + 1$ )t
c)		$μ t$
d)		$μ / t$

23. The equations of waves emitted by $S_{1}$ , $S_{2}$ , $S_{3}$ and $S_{4}$ are respectively
$Y_{1} = 20 \sin (100 π t)$
$Y_{2} = 20 \sin (200 π t)$
$Y_{3} = 10 \cos (100 π t)$
${and Y}_{4} = 20 \cos (100 π t)$
The phenomenon of interference will be produced by

a)		$Y_{1}$ and $Y_{2}$
b)		$Y_{2}$ and $Y_{3}$
c)		$Y_{1}$ and $Y_{3}$
d)		interference is not possible

24. Interference was observed in interference chamber, when air was present, if the chamber is evacuated and the same light is used, then we will see

a)		no interference
b)		interference with dark bands
c)		interference with bright bands
d)		interference in which breadth of the fringe will be slightly increased

25. A beam of monochromatic light is refracted from vacuum into a medium of refractive index 1.5. The wavelength of refracted light will be

a)		dependent on intensity of refracted light
b)		same
c)		smaller
d)		larger

26. What should be refractive index of a transparent medium to be visible in vacuum?

a)		1
b)		<1
c)		>1
d)		none of these

27. For what value of angle of incidence a ray incident on a glass plate ( $μ = 1.5)$ will the reflected ray and the refracted ray be perpendicular to each other?

a)		$∠ i = 45^{o}$
b)		$∠ i = 30^{o}$
c)		$∠ i = 40^{o}$
d)		$∠ i = 57^{o}$

28. Let you be sitting in sun for 2.5 hours. The area of your body exposed normally to sum rays is 1.3 $m^{2}$ . The intensity of sun rays is 1.1kW/ $m^{2}$ . If your body completely absorbs the sun rays then the momentum transferred to your body will be (in kg. m/s)

a)		0.043
b)		0.037
c)		0.61
d)		0.91

29. Two coherent sources of intensities $I_{1}$ and $I_{2}$ produce an interference pattern. The maximum intensity in the interference pattern will be

a)		$I_{1} + I_{2}$
b)		$I_{1}^{2} + I_{2}^{2}$
c)		${(I_{1} + I_{2})}^{2}$
d)		${(\sqrt{I_{1}} + \sqrt{I_{2}})}^{2}$

30. The first diffraction minima due to a single slit diffraction is at $θ = 30^{o}$ for a light of wavelength 500A. The width of the slit is

a)		5 $\times 10^{- 5}$ cm
b)		1.0 $\times 10^{- 5}$ cm
c)		2.5 $\times 10^{- 5}$ cm
d)		1.25 $\times 10^{- 5}$ cm

31. Two independent waves are expressed as $Y_{1}$ = $a_{1}$ sin $ω_{1} t$ and $Y_{2} = a_{2} \sin ω_{2} t,$ whether interference is possible with these

a)		yes
b)		no
c)		sometimes possible and sometimes not
d)		nothing can be predicted

32. In Young's double slit experiment, carried out with light od wavelength $λ = 5000 A$ , the distance between the slits is 0.2mm and the screen is at 200 cm from the slits. The central max is at x=0. The third max. (taking central max. as seroth max.) will be at x equal to

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

33. In a biprism experiment, by using light of wavelength 5000A, 5mm wide fringes are obtained on a screen 1.0m away from the coherent sources. The separation between the two coherent cources is

a)		1.0m
b)		0.1mm
c)		0.05mm
d)		0.01mm

34. In a Young's experiment, two coherent sources are placed 0.90mm apart and the fringes are observed one metre away. If it produces the second dark fringe at a distance of 1mm from the central fringe, the wavelength of monochromatic light used will be

a)		60 $\times 10^{- 4}$ cm
b)		10 $\times 10^{- 4}$ cm
c)		10 $\times 10^{- 5}$ cm
d)		6 $\times 10^{- 5}$ cm

35. In a medium, the source and the observer are both moving in the same direction with the same speed V. The apparent frequency $v^{'}$ is then related to the true frequency v by (speed of sound in the medium = c)

a)		$v^{'} = (\frac{1 - V / c}{1 + V / c})$ v
b)		$v^{'} = v$
c)		$v^{'} = \sqrt{1 - \frac{V^{2}}{c^{2}}}$ v
d)		$v^{'} = (\frac{1 + V / c}{1 - V / c})$ v

36. In a double slit interference experiment, the distance between the slits is 0.05 cm and screen is 2m away from the slits. The wavelength of light is 8.0 $\times 10^{- 5}$ cm. The distance between successive fringes is

a)		0.24 cm
b)		3.2 cm
c)		1.28 cm
d)		0.32 cm

37. The displacment of interfering waves are $Y_{1} =$ 4 sin $ω t$ cm and $Y_{2} =$ 3 sin ( $ω$ t+ $π$ /2) respectively. The amplitude of resultant will be

a)		5
b)		7
c)		1
d)		0

38. When a cotton cloth is put in front of eyes and a distant lighting bulb is viewed, the multiple bulbs are seen in a rectangular pattern around the bulb. The reason for this is

a)		the sight illusion
b)		a large number of holes in the cloth
c)		the small holes in the cloth behave like slits for light due to which a diffraction pattern is observed
d)		the size of the cloth is equal to that of bulb

39. The fringe width at a distance of 50cm be the slits in Young's expt. for light of wave length 6000 A is 0.048 cm. The fringe wave at the same distance for $λ = 5, 000$ A will be

a)		0.04 cm
b)		0.4 cm
c)		0.14 cm
d)		0.45 cm

40. Two coherent light sources $S_{1}$ and $S_{2}$ ( $λ$ =6000 A) are 1 mm apart from each other. The screen is placed at a distance of 25 cm from the sources. The width of the fringes on the screen should be

a)		0.015 cm
b)		0.025 cm
c)		0.010 cm
d)		0.030 cm

41. Wave length of a monochromatic light is 5000 Angstrom. Then its wave number is

a)		5000 $\times 10^{- 10}$ ${metre}^{- 1}$
b)		2 $\times 10^{5}$ ${metre}^{- 1}$
c)		2 $\times 10^{6}$ ${metre}^{- 1}$
d)		2 $\times 10^{4}$ ${metre}^{- 1}$

42. The correct formula for fringe visibility

a)		V = $\frac{I_{\max} - I_{\min}}{I_{\max} + I_{\min}}$
b)		V = $\frac{I_{\max} + I_{\min}}{I_{\max} - I_{\min}}$
c)		V = $\frac{I_{\max}}{I_{\min}}$
d)		V = $\frac{I_{\min}}{I_{\max}}$

43. At first diffraction pattern is obtained in red light, when white light is used then the fraction pattern

a)		shrink
b)		enlarge
c)		centre white
d)		none of these

44. Newton gave corpuscular theory on the basis of

a)		Newton's rings
b)		Rectilinear motion
c)		Certain corpuscles
d)		Wave front

45. If yellow light emitted by sodium lamp in Young's double slit expt. is replaced by mono-chromatic blue light of the same intensity

a)		fringe width will decrease
b)		fringe width will increase
c)		fringe width will remain unchanged
d)		fringes will become less intense

46. Motion of a wave front of a wave has direction with wave motion

a)		parallel
b)		perpendicular
c)		opposite
d)		at angle of $θ$

47. Which of the following statement is correct ?

a)		Diffraction is because of interference of light from same source whereas interference is due to light from two isolated sources
b)		Diffraction is due to interaction of light from same wave front whereas interference is due to interaction of two waves obtained from same source
c)		Diffraction is due to interference of wave derived from the same source whereas interference is bending of light from same source
d)		Diffraction is due to reflection waves whereas interference is due to transmitted waves, from a source

48. Path difference between two interfering waves at a point on the screen is $λ$ /8. The ratio of intensity at this point and that at the central fringe will be

a)		0.853
b)		8.53
c)		85.3
d)		853

49. A laser is a coherent source because it consists

a)		many values of wavelengths
b)		unco-ordinated waves of particular wavelength
c)		co-ordinated waves of many wave length
d)		co-ordinated waves of a particular wave length

50. The Fraunhofer diffraction pattern of a single slit is formed in the focal plane of a lens of focal length 1 m. The width of the slit is 0.3 mm. If third minimum is formed at a distance of 5 mm from central maximum, then wave length of light will be

a)		5000A
b)		2500A
c)		7500A
d)		8500A