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### Optics - MCQs

Optics - MCQs Points : optics mcqs, optics fill in the blanks, optics objective type questions 1. A lamp is hanging at a height 40 cm from the centre of a table. If its height is increased by 10 cm the illuminance on the table will decrease by
(a) 10%
(b) 20%
(c) 27%
(d) 36%

2. Inverse square law for illuminance is valid for
(a) isotropic point source
(b) acylindrical source
(c) a search light
(d) all types of sources

3. In a movie hail, the distance between the projector and the screen is increased by 1%. The illumination on the screen is
(a) increased by 1%
(b) descreased by 1%
(c) increased by 2%
(d) decreased by 2%

4. The first successful terrestrial determination of the speed of light was made by
(a) Fizeau
(b) Foucault
(c) Roemer
(d) Michelson

5. The distance between a point source of light and a screen is doubled. The intensity will be
(a) four times the original value
(b) two times the original value
(c) half the original value
(d) one quarter of the original value

6. The first laboratory determination of the speed of light was made by
(a) Fizeau
(b) Focault
(c) Roemer
(d) Michelson

7. The unit of luminous efficiency of an electric bulb is
(a) watt
(b) lumen
(c) lumen/watt
(d) lux.

8. The first unsuccessful attempt to determine the speed of light was made by
(a) Newton
(b) Roemer
(c) Galileo
(d) Fizeau

9. The velocity of light in diamond glass, and water decreases in the order
(a) water > glass > diamond
(b) diamond > glass> water
(c) diamond > water> glass
(d) water > diamond > glass

10. A light year is
(a) the time taken by the earth to go round the sun once
(b) the time taken by light to travel from the sun to the earth
(c) the distance travelled by light in one year
(d) a leap year

11. In a cinema hail, if the distance between the projector and the screen is increased by 2.5%, the intensity of illumination on the screen will be
(a) decreased by 25%
(b) decreased by 5%
(c) increased by 2.5%
(d) increased by 5%

12. A ray of light is incident on a plane mirror at an angle of incidence of 30°. The deviation produced
by the mirror is
(a) 30°
(b)
(c) 90°
(d) 120°

13. A virtual image, larger than the object can be produced by a
(a) convex mirror
(b) concave mirror
(c) plane mirror
(d) concave lens

14. A thick plane mirror shows a number of images of the filament of an electric bulb. Of these, the brighest image is the
(a) first
(b) second
(c) last
(d) fourth

15. 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 900 to each other

16. A plane mirror is approaching you at 10cm/s. You can see your image in it. At what speed will your image approach you?
(a) 10 cm/s
(b) 5 cm/s
(c) 20cm/s
(d) 15cm/s

17. The number of images observable between two parallel mirrors is
(a) 2
(b) 4
(c) 6
(d) infinite

18. The image of an object placed at a distance of 3m from a plane mirror has to be photographed. The camera, which is at a distance of 4.5m from the mirror should be focused for a distance of
(a) 3m
(b) 4.5m
(c) 6m
(d) 7.5m

19. A converging lens is that which
(a) collects rays
(c) forms a real image
(d) forms a virtual image

20. The picture seen on the screen of a pin-hole camera is
(a) an image
(c) neither an image nor a shadow
(d) both an image and a shadow

21. How many images of himself does an observer see if two adjacent walls and the ceiling of a rectangular room are mirror surfaced?
(a)3
(b) 5
(c) 6
(d) 9

22. light travels
(a) strictly in a straight line
(b) approximately in straight lines
(c) in a wavy form
(d) with infinite velocity

23. The image formed by a convex mirror of focal length 30 cm is quarter of the size of the object. The distance of the object from the mirror is
(a) 30cm
(b) 90cm
(c) 120cm
(d) 60cm

24. An object is put at a distance of 5 cm from the first focus of a convex lens of focal length 10 cm. If a real image is formed, its distance from the lens will be
(a) 15cm
(b) 20 cm
(c) 25 cm
(d) 30cm

25. The reflector for street light using an electric bulb should be
(a) plane
(b) spherical Concave
(c) spherical convex
(d) cylindrical concave

26. For street lighting the reflector used with an electric bulb should be a
(a) concave mirror
(b) convex mirror
(c) cylindrical mirror
(d) paraboloidal mirror

27. A person standing in front of a mirror finds his image larger than himself. This implies that the mirror
(a) plane.
(b) Convex
(c) concave
(d) cylindrical with bulging side Outwards

28. Two thin lenses of focal lengths 20cm and - 30cm are placed in contact with each other. The combination has a focal length of
(a) -10cm
(b) 50cm
(c) 60cm
(d) 10cm

29. An air bubble in water behaves as a
(a) convergent lens
(b) divergent lens
(c) cylindrical lens
(d) bifocal lens

30. The angle of a prism is 60° and its refractive index is 1.5. There will be no emergent light if the angle of incidence on the first face is
(a) equal to 30°
(b) less than 27°
(c) more than 30°
(d) equal to 60°

31. For a real object, a concave mirror always forms an image which is
(a) real and inverted
(b) virtual and inverted
(c) virtual and erect
(d) real and magnified

32. A convex lens of glass is immersed in water. Compared to its power in air, its power in water will
(a) diminish for red light and increase for blue light
(b) not change at all
(c) increase
(d) diminish

33. A decrease in the aperture of a lens changes
(a) the position of the image
(b) the size of the image
(c) the intensity of the image
(d) both the position and size of the image

34. When a thin convex lens is put in contact with a thin concave lens of the same focal length, the resultant combination has a focal length equal to
(a) f/2
(b) 21
(c) zero
(d) infinity

35. The angle of a prism is 6° and its refractive index for green light is 1.5. II a green ray passes through it, the deviation will be
(a) 30°
(b) 9°
(c) 15°
(d) 3°

36. A prism has a refracting angle of 60°. When placed in the position of minimum deviation, it produces a deviation of 30°.Thcn the angle of incidence is
(a) 30°
(b) 45°
(c) 15°
(d) 60°

37. A cut diamond sparkles because of
(a) its hardness
(b) its high refractive index
(c) emission of light by the diamond
(d) absorption of light by the diamond

38. If the angle of a prism is 60° and angle of minimum deviation is 40°, then the angle of refraction will be.
(a) 30°
(b) 60°
(c) 100°
(d) 120°

39. A monochromatic beam of light passes from a denser medium into a rarer medium. As a result its
(a) velocity increases
(b) velocity decreases
(c) frequency decreases
(d) wavelength decreases

40. The term refraction refers to the bending of light
(a) rays when they strike a mirror
(b) rays when they enter a different medium
(c) around a sharp edge
(d) around the boundary of a narrow aperture

41. With respect to its actual position, a bird in air appears to a fish in water
(a) to be nearer
(b) to be farther
(c) to be at its true distance
(d) neither nearer nor farther

42. When the moon is near the horizon, it appears bigger. This is due to
(a) atmospheric refraction
(b) scattering of light
(c) diffraction
(d) optical illusion

43. The ratio of the refractive index of red light to blue light in air is
(a) less than unity
(b) equal to unity
(c) greater than unity
(d) less as well as greater than unity depending upon the experimental arrangement

44. A completely transparent material will be invisible in vacuum when the refractive index u is
(a) unity
(b) more than unity
(c) less than unity
(d) equal to 1.33

45. The refractive index of a given piece of transparent quartz is the greatest for
(a) red light
(b) violet light
(c) green light
(d) yellow light

46. The critical angle of light passing from glass to air is minimum for
(a) red
(b) green
(c) yellow
(d) violet

47. An achromatic combination of lenses produces
(a) images in black and white
(b) coloured images
(c) images unaffected by variations of refractive index with wave length
(d) Highly enlarged images

48. The colour of light is characteristic of
(a) amplitude
(b) wavelength
(c) velocity
(d) frequency

49. Total internal reflection can occur when light passes from
(a) a denser to a rarer medium
(b) a rarer to a denser medium
(c) one medium to another of equal refractive index
(d) one medium to another of equal absorption coefficient

50. A piece of red glass is heated till it glows in the dark. The colour of the glowing piece will be
(a) red
(b) orange
(c) green
(d) violet

51. One cannot see through fog because
(a) fog absorbs light
(b) light is scattered by the droplets in a fog
(c) light suffers total reflection at the droplets in a fog
(d) the refractive index of fog is infinity

52. Which of the following statements is wrong?
(a) Light travels faster in vacuum than air
(b) The wavelength of light is longer than the wavelength of sound
(c) Sound travels nearly 330 metres in one second
(d) Speed of sound is ‘Mach number one’

53. A blue star is
(a) hotter than a white star
(b) cooler than a white star
(c) at the same temperature as a white star
(d) hotter or cooler than a white star depending upon its mass

54. The duration of day is increased by about four minutes due to the
(a) rotation of the earth
(b) atmosphere of the earth
(c) magnetic field of the earth
(d) rotation of the moon

55. It is possible to observe total internal reflection when a ray travels from
(a) air into water
(b) air into glass
(c) water into glass
(d) glass into water

56. A rainbow is produced by
(a) the refraction of light
(b) the reflection of light
(c) the diffraction of light
(d) both a and b

57. Mirages are observed in deserts due to the phenomenon of
(a) interference of light
(b) total reflection of light
(c) scattering of light
(d) double refraction of light

58. The colour of a star is an indication of
(a) weight
(b) distance
(c) temperature
(d) size

59. When blue light falls on a lump of sodium, the lump is found to
(a) have acquired high temperature
(b) have become very cold
(c) emit electrons each having different energies
(d) emits electrons each having the same energy

60. Which of the following produces additional luminiscence in a fluorescent tube?
(a) Infrared rays
(b) ultraviolet trays
(c) Microwaves

61. A red flower kept in the green light will appear
(a) red
(b) green
(c) black
(d) white

62. The blue colour of the sky is due to
(a) scattering of light
(b) dispersion of light
(c) interference
(d) the reason that the sun emits more of blue light

63. In a room fitted with a green bulb, a red cloth will appear to be
(a) yellow
(b) orange
(c) black
(d) blue

64. If the sky is seen from the moon’s surface it will appear
(a) blue
(b) black
(c) white
(d) red

65. At sunrise or sunset the sun looks redder than at midday because
(a) the sun is hottest at these times
(b) of the scattering of light
(c) of the effects of refraction
(d) of the effects of diffraction

66. When light is extremely faint, the maximum sensitivity of the eye is in the
(a) red light
(b) yellow-green light
(c) blue-green light
(d) red-green light

67. Emission of light stops as the incident light is cu off in
(a) phosphorescence
(b) fluorescence
(c) luminescence
(d) efflorescence

68. Chromatic aberration in a lens is caused by
(a) reflection
(b) interference
(c) diffraction
(d) dispersion

69. Colours of a stained glass window are due to
(a) interference of light
(b) diffraction of light
(c) polarisation of light
(d) scattering of light

70. When a beam of white light falls on an achromatic combination of prisms, then there is
(a) deviation only
(b) dispersion only
(c) deviation and dispersion both
(d) neither deviation nor dispersion

71. Chromatic aberration of a lens is
(a) not dependent on focal length
(b) directly proportional to focal length
(c) inversely proportional to focal length
(d) inversely proportional to dispersive power

72. Fingerprints on paper are identified liy sprinkling fluorescent powder on it and observing it under
(a) mercury light
(b) sun light
(c) infrared light
(d) ultraviolet light

73. An endoscope is a
(a) narrow telescope
(b) type of camera
(c) simple microscope
(d) none of these

74. The light which enters the human eye experiences most of its refraction while passing through the
(a) cornea
(b) aqueous humor
(c) vitreous humor
(d) crystalline lens

75. The ability of the eye to focus on both near and far objects is called
(a) myopia
(b) hypermetropia
(c) presbyopia
(d) accommodation

76. The final image produced by a compound microscope is
(a) real and erect
(b) virtual and erect
(c) virtual and inverted
(d) real and inverted

77. A cylindrical lens is required to correct
(a) myopia
(b) presbyopia
(c) hypermetropia
(d) astigmatism

78. A myopic patient uses
(a) convex lens
(b) concave lens
(c) cylindrical lens
(d) bifocal lens

79. A person suffering from hypermetropia used
(a) convex tens
(b) concave lens
(c) cylindrical lens
(d) bifocal lens

80. Loss of the ability of eye to focus on near and far objects with advancing age is called
(a) presbyopia
(b) astigmatism
(c) hypermetropia
(d) myopia

81. The aperture of a telescope objective is increased to produce a
(a) larger image
(b) smaller spherical aberration
(c) small chromatic aberration
(d) larger resolving power

82. An individual with one eye is likely to
(a) have stereoscopic vision
(b) have binocular vision
(c) misjudge distances
(d) have stroboscopic vision

83. A sextant is used to measure the
(a) area of a mountain
(c) height of an object
(d) volume of a building

84. Large apertures in telescopes are used for
(a) greater magnification
(b) greater resolution
(c) reducing lens aberrations
(d) case of manufacture

85. A reflecting telescope utilises
(a) a concave mirror
(b) a convex mirror
(c) a prism
(d) a pIano convex lens

86. Sextant is so called because
(a) it was invented by Sextant
(b) it has six components
(c) its scale is 1/6 of a circle
(d) none of the above

87. A simple microscope uses
(a) a convex lens of small focal length
(b) a concave lens of small focal length
(c) a convex lens of large focal length
(d) a concave lens of large focal length

88. The simple microscope was first made by by
(a) robert Hook
(b) leuwenhoek
(c) splanzni
(d) jenner

89. In myopia
(a) the image is formed in front of the retina
(b) the image is formed behind the retina
(c) the image is formed on the retina
(d) no image is formed

90. The final image produced by a simple microscope is
(a) rirtual and erect
(b) virtual and inverted
(c) real and erect
(d) real and inverted

91. Newton postulated his corpuscular theory on the basis of
(a) Newton’s rings
(b) rectilinear propagation of light
(c) colours through this films
(d) dispersion of white light into colours

92. In a direct vision spectroscope, one uses
(a) interference without deviation
(b) deviation without interference
(c) deviation without dispersion
(d) dispersion without deviation

93. The image of a distant object as seen through an astronomical telescope is
(a) erect
(b) inverted
(c) perverted
(d) none of the above

94. The focal length of the lens in the human eye is maximum when it is looking at an object at
(a) infinity
(b) 25 cm from the eye
(c) 100 cms from the eye
(d) a very small distance from the eye

95. The length of a simple astronomical telescope is
(a) the difference of the focal lengths of the two lenses
(b) half the sum of the focal lengths
(c) the sum of the focal lengths
(d) product of the focal lengths

96. The magnifying power of a telescope can be increased by
(a) increasing the focal length
(b) fitting an eyepiece of high power
(c) fitting an eyepiece of low power
(d) increasing the distance of the object

97. In an astronomical telescope, the final image for normal vision Is formed at
(a) the least distance of distinct vision
(b) at the focus of the objective lens
(c) at the focus of the eye lens
(d) at infinity

98. A photographer changes the aperture of his camera and reduces it to half of the original aperture. The exposure time now should be
(a) same as before
(b) double than before
(c) four times than before
(d) half

99. How should people wearing spectacles work with a microscope?
(a) they should keep on wearing their spectacles
(b) they should take off their spectacles
(c) they may keep on wearing or take off their spectacles, it makes no difference
(d) they cannot use a microscope at all

100. The fringe pattern observed in a Young’s double slit experiment is
(a) a diffraction pattern
(b) an interference pattern
(c) a combination of diffraction and interference pattern
(d) neither a diffraction nor an interference pattern

101. An electron microscope is superior to an optical microscope in
(a) having better resolving power
(b) being easy to handle
(c) costing less
(d) quickness of observation

102. The fringe width in a Young’s double slit experiment can be increased ii we decrease the
(a) separation of the slits
(b) width of the slits
(c) distance between slit and screen
(d) wavelength of the source light

103. 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

104. The illuminance on a small screen placed 2m from a 60 candela lamp is
(a) 240 lux
(b) 60 lux
(c) 15 Iux
(d) 90 lux

105. In the interference pattern, energy is
(a) created at the positions of maxima
(b) destroyed at the positions of minima
(c) conserved but is redistributed
(d) none of the above

106. Which of the following is not electromagnetic in nature?
(a) Infrared rays
(b) Ultraviolet rays
(d) Sound waves

107. A monochromatic visible light consists of
(a) a single ray of light
(b) light of a single wavelength
(c) light of a single wavelength with all the colours of the spectrum of white light
(d) light consisting of many wavelengths with a single colour

108. Young’s experiment establishes that light
(a) consists of waves
(b) consists of particles
(c) is neither particles nor waves
(d) is both particles and waves

109. Colours of thin films result from
(a) dispersion of light
(b) interference of light
(c) absorption of light
(d) scattering of light

110. When viewed in white light, soap bubbles show colour because of
(a) interference
(b) scattering
(c) diffraction
(d) dispersion