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Physics Lights and Optics Online Mcqs Test

Maan AliLast Updated: October 13, 2025

Important Lights and Optics Question and Answer

Total Questions:	88
Time Allowed:	40 Minutes
Total Marks:	88
How to Attempt Test:	Please choose the right Option in MCQ-type question.
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Physics Lights and Optics Practice Test Online With Explanation

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Page 1 of 4

Physics

1. Due to Plano convex lens and the plane glass plate the thickness of air film changes from the center to outward

None of these

Increasing gradually

It is constant at the center

Decreasing gradually

2. To demonstrate the phenomenon of interference we require two sources that emit radiation

Of same frequency

Different wavelength

Of the same frequency and having definite phase relationship

Of nearly the same frequency

3. Huygen’s wave theory of light cannot explain

Polarization

Diffraction

Interference

Photoelectric effect

4. A spectrum which contains all wavelengths without any break is called

Line spectrum

Emission spectrum

Continuous emission spectrum

All of these

5. A polarizer is used to

Produce unpolarised light

Reduced intensity of light

Increase intensity of light

Produce polarized light

6. The condition for constructive interference of two coherent beams is that the path difference should be

Integral multiple of λ

Integral multiple of λ/2

Even integral multiple of λ

Odd integral multiple of λ/2

7. The condition for the bright fringes formed due to constructive interference in a diffraction grating is:

d sin θ = mλ

md cos θ = λ

d sin θ = m/2 λ

d sin θ = 2λm

8. Longitudinal waves do not exhibit

Diffraction

Polarization

Refraction

Reflection

9. Huygen’s wave theory of light cannot explain

Polarization

Interference

Photoelectric effect

Diffraction

10. A spherical wave front is that which has

A extended source

None of these

A source

A point source

11. When crest of one wave falls over the trough of the other wave this phenomenon is known as

Diffraction

Destructive interference

Constructive interference

Polarization

12. Which of the following properties show light is transverse wave in nature?

Diffraction

Interference

Reflection

Polarization

13. The light produced by a laser is all the following except

Electromagnetic

In the form of a narrow beam

Monochromatic

Incoherent

14. Wave front is the locus of all points in vibration are in the same

Phase

Wavelength

Frequency

All of these

15. Light appears to travel in straight lies since

Its wavelength is very small

It is reflected by the atmosphere

It is not absorbed by the atmosphere

Its velocity is very large

16. The principle of Michelson’s interferometers is

Dispersion

Refraction

Interference

Reflection

17. In a plane polarized light

Vibration in all direction

No vibration at all

Vibration take place in a direction perpendicular to the direction of propagation of light

Vibration in two mutually perpendicular directions

18. When the light is incident on polarizing angle which of the following is completely polarized?

Refracted light

Reflected light

Neither reflected nor refracted light

Both reflected and refracted light

19. If a source of light is moving away from stationary observer, then frequency of light wave appears to change because of

Diffraction

Doppler’s effect

Interference

None of these

20. Intensities of the two waves of light are l and 4l. The maximum intensity of the resultant wave after superposition is

25l

16l

21. A ____________ lens is used to form Newton’s rings.

Double-convex

Plano-convex

Plano-concave

Convexo-concave

22. A diffraction grating has 500 lines per mm. Its slit spacing or grating element will be equal to

2 x 10¯³ mm

5 x 10¯³ mm

2 x 10¯⁵ mm

500 mm

23. Diffraction fringes are

Equally spaced

They are adjacent with no space in between

Distance between them increases

Distance between then decreases

24. In Young double slit experiment, if white light is used

Impossible to predict

No interference fringes will be seen

Alternate dark and bright fringes will be seen

Colored fringes will be seen

25. A thin film is a transparent medium whose thickness with the wavelength of light are

Both

Not comparable

None of these

Comparable

Page 2 of 4

26. Two sources of light are coherent if they emit rays of

Same wave length with constant phase difference

Same wavelength

Same amplitude and wavelength

Same amplitude of vibration

27. The cause of mirage observed in desert is

Total internal reflection

Refraction

Scattering

Reflection

28. Which effect provides direct experimental evidence that light is a transverse, rather than a longitudinal, wave motion?

Two coherent light waves can be made to interfere

Light can be diffracted

The intensity of light from a point source falls off inversely as the square of the distance from the source

Light can be polarized

29. Which one of the following phenomena is not explained by Hygen’s construction of wave front?

Refraction

Diffraction

Reflection

Origin of spectra

30. Interference was observed in interference chamber, when air was present, now the chamber is evacuated and if the same light is used, a careful observer will see

Interference with bright bands

Interference with dark bands

Interference in which breadth of the fringe will be slightly increase

No interference

31. Diffraction effect is

More for a round edge

Less for a sharp edge

Less for a round edge

More for a sharp edge

32. The fringe spacing in case of blue light

Increases

None of these

Decrease

Remains the same

33. On a rainy day, if there is an oil drop on tar road, colored rings are seen around this drop. This is because of

Total internal reflection of light

Polarization

Interference pattern produced due to thin oil film

Diffraction pattern

34. The contrast in the fringes in any interference pattern depends on

Wavelength

Fringe width

Distance between the slits

Intensity ratio of the sources

35. Which of the following frequency ranges includes most of the electromagnetic waves emitted by the ultra – violet tubes used in a sun bed?

5 x 10⁵ to 5 x 10⁵ Hz

5 x 10⁵ to 5 x 10¹¹ Hz

5 x 10¹¹ to 5 x 10¹⁴ Hz

5 x 10¹⁴ to 5 x 10¹⁷ Hz

36. An oil surface floating on water surface exhibits beautiful colour patter, which is due to

Reflection of light

None of these

Diffraction of light

Interference of light

37. The locus of all points in a medium having the same phase of vibration is called

Trough

Wave front

Crest

Wavelength

38. According to Huygen, every point on a wave front may be regarded as a __________ of secondary wavelets.

Producer

Source

Base

Origin

39. Central spot of New tons rings

Bright

Dart for large wavelength

Bright for large wavelength

Dark

40. Huygen’s wave fronts which sends out secondary wavelets with a speed equal to

Speed of propagation greater than wave

Speed of propagation less than the wave

Speed of propagation of the wave

B and C

41. In the Michelson Interferometer, if m number fringes pass through a reference point when the mirror is moved a distance d, then the wavelength of the light can be found by the formula:

λ = 2d/m

2λ = dm

λ = dm

λ = 2π dm

42. In an interference pattern

Both dark and bright fringes are of equal width

Dark fringes are wider than bright fringe

Bright fringes are wider than dark fringes

Central fringes are brighter than the outer fringes

43. The setting of Newton’s rings is

A Plano convex lens and the plane glass plate

None of these

A Plano convex lens (long focal length) and the plane of glass plate

A Plano convex lens and simple glass sheet

44. Ray optics is valid, when characteristic dimensions are

Of the order of one millimeter

Much smaller than the wavelength of length

Much larger than the wavelength of light

Of the same order as the wavelength of light

45. Which effect provides direct experimental evidence that light is a transverse, rather than a longitudinal, wave motion?

Two coherent light waves can be made to interfere

The intensity of light from a point source falls off inversely as the square of the distance from the source

Light can be diffracted

Light can be polarized

46. Wavelength of light of frequency 100 Hz is

4 x 10⁶ m

2 x 10⁶ m

5 x 10⁶ m

3 x 10⁶ m

47. In Michelson interferometer to switch the fringe from bright to dark the mirror should be displaced through

?/4

?/6

?/3

?/2

48. One condition for interference is that the two sources should be coherent and:

Opposite to each other

At a far off distance

Coinciding

Close together

49. Every point of a wave front may be considered as a

None of these

Source

Source of wave front

Source of secondary wave front

50. Coherent monochromatic light illuminates two narrow parallel slits and the interference pattern that results is observed on a screen some distance beyond the slits. Which modification increases the separation between the dark lines of the interference pattern?

Decreasing the distance between the screen and the slits

Increasing the distance between the slits

Using monochromatic light of longer wavelength

Using monochromatic light of higher frequency

Page 3 of 4

51. When the two surfaces of a thin film are parallel and the light is incident at a certain angle, _________ fringes are formed.

Circular

Parabolic

Straight

Elliptical

52. A point source of light placed in a homogeneous medium gives rise to

An elliptical wave front

A plane wave front

A spherical wave front

A cylindrical wave front

53. Crystals of a material can behave as

Concave

Interferometer

Convex lens

Diffraction grating

54. Which one of the following phenomena is not explained by Huygen’s construction of wave front?

Origin of spectra

Reflection

Diffraction

Refraction

55. Polarization occurs only in ________ waves

Transverse

Longitudinal

Matter waves

Mechanical waves

56. If the path difference must be half-integral number wavelength

d sin θ = (m + 1)λ

d sin θ = (m + 1/2)λ

d in θ = (m + ½ )1/λ

d sin θ = (m + 1/2)π/λ

57. Can two head lights of car can produce interference

Partly produce interference

None of these

Yes

58. In the phenomenon of interference, the bright ad dark fringes are of

Equal width

None of these

Different width

Dark fringes are thicker than bright

59. On a rainy day, if there is an oil drop on tar road, colored rings are seen around this drop. This is because of

Polarization

Total internal reflection of light

Interference pattern produced due to thin oil film

Diffraction pattern

60. Fraunhoffer’s lines commonly visible in the sun’s spectrum are examples of

Band emission spectrum

Band absorption spectrum

Line absorption spectrum

Line emission spectrum

61. The idea of light as wave produced by

Newton

Thomos young

Michelson

Huygen

62. According to the electromagnetic theory, the speed of light is approximately:

3 x 10¯¹⁰ ms¯¹

3 x 10⁸ ms¯¹

3.1 x 10⁸ ms¯¹

3 x 10⁵ ms¯¹

63. Curtain less windows are made by making use of __________ of light.

Diffraction

Absorption

Polarization

Transmission

64. Which of the following is conserved when light waves interfere?

Amplitude

Intensity

Momentum

Energy

65. Choose the correct statement

Rays are normal to wave front

Rays are not normal to wave front

There is no relationship between rays and wave fronts

Rays may be normal to wave front

66. Signal from a remote control to the device operated by it tracels with the speed of:

Sound

Supersonics

Light

Ultrasonics

67. The relation of constructive interference in X-ray diffraction is called

Laue’s pattern

Compton effect

Huygen’s formula

Bragg’s law

68. Why laser rays are used to measure long distance?

Laser rays are not absorbed

Laser rays are high velocity waves

Laser rays propagate in a straight line

Laser rays are most coherent waves

69. The light produced by a laser is all the following except

Electromagnetic

In the form of a narrow beam

Incoherent

Monochromatic

70. If a wave can be polarized, it must be

An electromagnetic wave

A transverse waves

A longitudinal wave

A sound wave

71. The blue colour of the sky is due to

Scattering

Reflection

Polarization

Diffraction

72. A prism splits a beam of white light into its seven constituent colors. This is so because

Amplitude of different colors is different

Velocity of different colors is different

Phase of different colors is different

Energy of different colors is different

73. In Newton’s rings the point of contact of the lend and the glass plate, the air film is

Maximum

None of these

Minimum

Zero

74. The splitting of white light into several colors on passing through a glass prism is due to

Diffraction

Interference

Refraction

Reflection

75. For the sustained interference of light, the necessary condition is that the two sources should

Of same amplitude

Be narrow

Have constant phase difference

Be close to each other

Page 4 of 4

76. In Young’s experiment, a dark fringe is observed when:

½ d Sin θ = mλ

d Sin θ = (m + 1/2)λ

m Sin θ = (d + 1/2)λ

2π Sin θ = (m + 1/2)λ

77. The phenomenon of bending of light waves around the edges of an obstacle or a narrow opening is called.

Transmission

Reflection

Diffraction

Refraction

78. If the dark fringe is to be observed then we have relation

Y = (m + 1/2) λd/L

Y = (m + 1/2) λL/d

Y = (m + ½) dL/λ

Y = (m + 1) λL/d

79. The locus of all points in the same phase of vibration is called:

Wavelength

Wave number

Wave form

Wave front

80. Light on passing through a Polaroid is

Plane polarized

Circularly polarized

Elliptically polarized

Un-polarized

81. Who devise the experimental arrangement is 1801 for studying interference effects of light?

Huygen

Newton

Young

None of these

82. Ultra – violet rays differ from X-rays in that ultra – violet rays

Cannot be polarized

Do not affect a photographic plate

Cannot be diffracted

Have a lower frequency

83. Which of the following has least wavelength?

γ-rays

Ultra-violet rays

X-rays

Cosmic-rays

84. Light is a type of energy which produces sensation of

Sound

Vision

Feeling

None of these

85. Which one of the following cannot be polarized?

Sound waves

Ultraviolet rays

X-rays

Radio waves

86. For constructive interference the path difference is

m²λ

(m – 1)λ

Mλ

½ mλ

87. In Huygen’s wave theory, the locus of all points in the same state of vibration is called

Vibrator

A half-period zone

A ray

Wave front

88. Appearance of colour in thin films is due to

Interference

Diffraction

Polarization

Dispersion

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Maan AliLast Updated: October 13, 2025

5 Comments

Trendsetter says:

September 5, 2021 at 2:27 pm

Idea of light as a wave was proposed by Huygen not young.

The best says:

June 30, 2020 at 5:40 pm

Light is a type of energy which produces sensation of vision.

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Physics Lights and Optics Online Mcqs Test

Important Lights and Optics Question and Answer

Physics Lights and Optics Practice Test Online With Explanation

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