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

Diffraction pattern

Polarization

Interference pattern produced due to thin oil film

Total internal reflection of light

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

Line absorption spectrum

Band emission spectrum

Line emission spectrum

Band absorption spectrum

3. The fringe spacing in case of blue light

Remains the same

None of these

Increases

Decrease

4. 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?

Using monochromatic light of higher frequency

Decreasing the distance between the screen and the slits

Increasing the distance between the slits

Using monochromatic light of longer wavelength

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

Do not affect a photographic plate

Cannot be diffracted

Have a lower frequency

Cannot be polarized

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

Close together

Coinciding

Opposite to each other

At a far off distance

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

Continuous emission spectrum

All of these

Line spectrum

Emission spectrum

8. In a plane polarized light

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

Vibration in all direction

No vibration at all

Vibration in two mutually perpendicular directions

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

5 x 10¯³ mm

500 mm

2 x 10¯³ mm

2 x 10¯⁵ mm

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

d Sin θ = (m + 1/2)λ

m Sin θ = (d + 1/2)λ

2π Sin θ = (m + 1/2)λ

½ d Sin θ = mλ

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

It is constant at the center

Increasing gradually

None of these

Decreasing gradually

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

Polarization

Diffraction

Constructive interference

Destructive interference

13. A polarizer is used to

Reduced intensity of light

Produce unpolarised light

Increase intensity of light

Produce polarized light

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

Light can be polarized

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

Two coherent light waves can be made to interfere

Light can be diffracted

15. Diffraction fringes are

Distance between then decreases

Distance between them increases

They are adjacent with no space in between

Equally spaced

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

Straight

Elliptical

Parabolic

Circular

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

Colored fringes will be seen

No interference fringes will be seen

Alternate dark and bright fringes will be seen

Impossible to predict

18. Central spot of New tons rings

Bright for large wavelength

Dark

Bright

Dart for large wavelength

19. 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

20. Longitudinal waves do not exhibit

Polarization

Refraction

Diffraction

Reflection

21. The blue colour of the sky is due to

Scattering

Diffraction

Reflection

Polarization

22. The idea of light as wave produced by

Michelson

Huygen

Newton

Thomos young

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

25l

16l

24. 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 10¹¹ Hz

5 x 10¹⁴ to 5 x 10¹⁷ Hz

5 x 10⁵ to 5 x 10⁵ Hz

5 x 10¹¹ to 5 x 10¹⁴ Hz

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

Same wavelength

Same wave length with constant phase difference

Same amplitude of vibration

Same amplitude and wavelength

Page 2 of 4

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

Light

Sound

Supersonics

Ultrasonics

27. Ray optics is valid, when characteristic dimensions are

Of the same order as the wavelength of light

Much larger than the wavelength of light

Of the order of one millimeter

Much smaller than the wavelength of length

28. Light appears to travel in straight lies since

It is not absorbed by the atmosphere

Its velocity is very large

It is reflected by the atmosphere

Its wavelength is very small

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

Velocity of different colors is different

Amplitude of different colors is different

Energy of different colors is different

Phase of different colors is different

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

Intensity

Momentum

Energy

Amplitude

31. 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

No interference

Interference with dark bands

Interference with bright bands

Interference in which breadth of the fringe will be slightly increase

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

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

Light can be diffracted

Two coherent light waves can be made to interfere

Light can be polarized

33. For constructive interference the path difference is

Mλ

m²λ

(m – 1)λ

½ mλ

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

3 x 10⁵ ms¯¹

3 x 10¯¹⁰ ms¯¹

3.1 x 10⁸ ms¯¹

3 x 10⁸ ms¯¹

35. In an interference pattern

Bright fringes are wider than dark fringes

Both dark and bright fringes are of equal width

Central fringes are brighter than the outer fringes

Dark fringes are wider than bright fringe

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

Have constant phase difference

Be narrow

Be close to each other

Of same amplitude

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

Y = (m + 1) λL/d

Y = (m + ½) dL/λ

Y = (m + 1/2) λd/L

Y = (m + 1/2) λL/d

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

Interference

Doppler’s effect

Diffraction

None of these

39. Appearance of colour in thin films is due to

Polarization

Diffraction

Dispersion

Interference

40. A spherical wave front is that which has

A point source

A source

A extended source

None of these

41. The cause of mirage observed in desert is

Refraction

Reflection

Scattering

Total internal reflection

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

Wavelength

Distance between the slits

Fringe width

Intensity ratio of the sources

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

Wave front

Vibrator

A ray

A half-period zone

44. The principle of Michelson’s interferometers is

Refraction

Dispersion

Interference

Reflection

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

d sin θ = (m + 1)λ

d sin θ = (m + 1/2)λ

d sin θ = (m + 1/2)π/λ

d in θ = (m + ½ )1/λ

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

Sound

None of these

Feeling

Vision

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

An elliptical wave front

A plane wave front

A cylindrical wave front

A spherical wave front

48. The setting of Newton’s rings is

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

A Plano convex lens and the plane glass plate

A Plano convex lens and simple glass sheet

None of these

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

Wavelength

Wave front

Wave form

Wave number

50. Which one of the following cannot be polarized?

Sound waves

Ultraviolet rays

Radio waves

X-rays

Page 3 of 4

51. Polarization occurs only in ________ waves

Mechanical waves

Transverse

Longitudinal

Matter waves

52. Huygen’s wave theory of light cannot explain

Polarization

Photoelectric effect

Interference

Diffraction

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

Even integral multiple of λ

Integral multiple of λ/2

Integral multiple of λ

Odd integral multiple of λ/2

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

Phase

Frequency

Wavelength

All of these

55. Crystals of a material can behave as

Diffraction grating

Interferometer

Convex lens

Concave

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

Maximum

Minimum

Zero

None of these

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

Absorption

Transmission

Diffraction

Polarization

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

d sin θ = 2λm

d sin θ = mλ

d sin θ = m/2 λ

md cos θ = λ

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

Reflection

Diffraction

Interference

Refraction

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

Source of secondary wave front

None of these

Source

Source of wave front

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

Origin

Producer

Base

Source

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

?/2

?/3

?/6

?/4

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

Diffraction

Refraction

Transmission

Reflection

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

Interference of light

Reflection of light

None of these

Diffraction of light

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

Diffraction

Refraction

Reflection

Origin of spectra

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

Electromagnetic

Incoherent

Monochromatic

In the form of a narrow beam

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

Origin of spectra

Diffraction

Refraction

Reflection

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

Not comparable

Comparable

Both

None of these

69. Wavelength of light of frequency 100 Hz is

4 x 10⁶ m

3 x 10⁶ m

2 x 10⁶ m

5 x 10⁶ m

70. Huygen’s wave theory of light cannot explain

Polarization

Photoelectric effect

Interference

Diffraction

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

Wavelength

Crest

Wave front

Trough

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

In the form of a narrow beam

Incoherent

Monochromatic

Electromagnetic

73. Diffraction effect is

Less for a sharp edge

Less for a round edge

More for a round edge

More for a sharp edge

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

A transverse waves

An electromagnetic wave

A sound wave

A longitudinal wave

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

Bragg’s law

Compton effect

Laue’s pattern

Huygen’s formula

Page 4 of 4

76. 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

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

Diffraction

Interference

Reflection

Polarization

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

Speed of propagation of the wave

B and C

Speed of propagation less than the wave

Speed of propagation greater than wave

79. Can two head lights of car can produce interference

None of these

Partly produce interference

Yes

80. Which of the following has least wavelength?

Cosmic-rays

Ultra-violet rays

X-rays

γ-rays

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

Convexo-concave

Plano-convex

Double-convex

Plano-concave

82. Choose the correct statement

There is no relationship between rays and wave fronts

Rays may be normal to wave front

Rays are normal to wave front

Rays are not normal to wave front

83. 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:

2λ = dm

λ = 2π dm

λ = dm

λ = 2d/m

84. Light on passing through a Polaroid is

Circularly polarized

Elliptically polarized

Plane polarized

Un-polarized

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

Neither reflected nor refracted light

Reflected light

Refracted light

Both reflected and refracted light

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

Laser rays are most coherent waves

Laser rays are not absorbed

Laser rays are high velocity waves

Laser rays propagate in a straight line

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

None of these

Equal width

Dark fringes are thicker than bright

Different width

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

Huygen

Young

None of these

Newton

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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.

Chaudry Adnan says:

August 24, 2017 at 5:13 pm

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Abuzar says:

April 26, 2017 at 11:07 am

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umair ahmed says:

March 21, 2017 at 1:26 am

if some is one is using this website so plz reply

Important Lights and Optics Question and Answer

Physics Lights and Optics Practice Test Online With Explanation

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