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ECAT Physics Lights and Optics Online Test

Maan AliLast Updated: April 18, 2025

Physics Lights and Optics MCQS Online Test

ECAT Physics Lights and Optics Chapter Online Test

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 Chapter Online Test

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Page 1 of 4

Physics

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

Equal width

None of these

Dark fringes are thicker than bright

Different width

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

Intensity

Energy

Momentum

Amplitude

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

Interference

Polarization

Reflection

Diffraction

4. Crystals of a material can behave as

Concave

Convex lens

Interferometer

Diffraction grating

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

Diffraction

Transmission

Refraction

Reflection

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

Energy of different colors is different

Phase of different colors is different

Velocity of different colors is different

Amplitude of different colors is different

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

?/2

?/4

?/3

?/6

8. A spherical wave front is that which has

None of these

A extended source

A point source

A source

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

Incoherent

Electromagnetic

Monochromatic

In the form of a narrow beam

10. Can two head lights of car can produce interference

Yes

None of these

Partly produce interference

11. The cause of mirage observed in desert is

Scattering

Total internal reflection

Reflection

Refraction

12. In a plane polarized light

No vibration at all

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

Vibration in two mutually perpendicular directions

Vibration in all direction

13. 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 longer wavelength

Decreasing the distance between the screen and the slits

Increasing the distance between the slits

Using monochromatic light of higher frequency

14. 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

15. Polarization occurs only in ________ waves

Longitudinal

Mechanical waves

Matter waves

Transverse

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

Diffraction

Origin of spectra

Refraction

Reflection

17. A polarizer is used to

Produce unpolarised light

Produce polarized light

Increase intensity of light

Reduced intensity of light

18. 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 polarized

Light can be diffracted

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

19. 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

Diffraction pattern

Interference pattern produced due to thin oil film

Polarization

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

500 mm

5 x 10¯³ mm

2 x 10¯⁵ mm

2 x 10¯³ mm

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

Y = (m + ½) dL/λ

Y = (m + 1) λL/d

Y = (m + 1/2) λL/d

Y = (m + 1/2) λd/L

22. 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

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

Refraction

Reflection

Origin of spectra

Diffraction

24. 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

None of these

Increasing gradually

Decreasing gradually

25. 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 = 2λm

d sin θ = m/2 λ

Page 2 of 4

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

Frequency

All of these

Wavelength

Phase

27. Light on passing through a Polaroid is

Plane polarized

Elliptically polarized

Un-polarized

Circularly polarized

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

Incoherent

Monochromatic

Electromagnetic

In the form of a narrow beam

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

Reflection of light

None of these

Interference of light

Diffraction of light

30. 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 = 2d/m

λ = dm

31. For constructive interference the path difference is

½ mλ

m²λ

(m – 1)λ

Mλ

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

None of these

Source of secondary wave front

Source of wave front

Source

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

Convexo-concave

Plano-convex

Plano-concave

Double-convex

34. 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

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

Alternate dark and bright fringes will be seen

No interference fringes will be seen

Colored fringes will be seen

Impossible to predict

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

Close together

At a far off distance

Opposite to each other

Coinciding

37. 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 10¹⁴ to 5 x 10¹⁷ Hz

5 x 10⁵ to 5 x 10⁵ Hz

5 x 10¹¹ to 5 x 10¹⁴ Hz

5 x 10⁵ to 5 x 10¹¹ Hz

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

A cylindrical wave front

A plane wave front

A spherical wave front

An elliptical wave front

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

Straight

Parabolic

Circular

Elliptical

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

Wavelength

Distance between the slits

Intensity ratio of the sources

Fringe width

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

Integral multiple of λ

Odd integral multiple of λ/2

Even integral multiple of λ

Integral multiple of λ/2

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

Constructive interference

Diffraction

Destructive interference

Polarization

43. Which one of the following cannot be polarized?

Radio waves

Sound waves

Ultraviolet rays

X-rays

44. Light appears to travel in straight lies since

It is reflected by the atmosphere

It is not absorbed by the atmosphere

Its velocity is very large

Its wavelength is very small

45. 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 in which breadth of the fringe will be slightly increase

No interference

Interference with bright bands

Interference with dark bands

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

Young

None of these

Huygen

Newton

47. The idea of light as wave produced by

Newton

Huygen

Thomos young

Michelson

48. Huygen’s wave theory of light cannot explain

Diffraction

Photoelectric effect

Interference

Polarization

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

Of the same frequency and having definite phase relationship

Of same frequency

Different wavelength

Of nearly the same frequency

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

Diffraction

Absorption

Polarization

Transmission

Page 3 of 4

51. The fringe spacing in case of blue light

None of these

Decrease

Remains the same

Increases

52. Huygen’s wave theory of light cannot explain

Diffraction

Photoelectric effect

Interference

Polarization

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

Vision

None of these

Feeling

Sound

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

Emission spectrum

All of these

Line spectrum

Continuous emission spectrum

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

Interference pattern produced due to thin oil film

Polarization

Total internal reflection of light

Diffraction pattern

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

Speed of propagation of the wave

Speed of propagation greater than wave

Speed of propagation less than the wave

B and C

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

Crest

Wave front

Wavelength

Trough

58. Central spot of New tons rings

Bright

Bright for large wavelength

Dark

Dart for large wavelength

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

3 x 10⁸ ms¯¹

3.1 x 10⁸ ms¯¹

3 x 10¯¹⁰ ms¯¹

3 x 10⁵ ms¯¹

60. 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

61. Wavelength of light of frequency 100 Hz is

4 x 10⁶ m

2 x 10⁶ m

3 x 10⁶ m

5 x 10⁶ m

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

Reflected light

Both reflected and refracted light

Neither reflected nor refracted light

Refracted light

63. Diffraction effect is

Less for a sharp edge

More for a sharp edge

Less for a round edge

More for a round edge

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

d sin θ = (m + 1/2)λ

d sin θ = (m + 1/2)π/λ

d sin θ = (m + 1)λ

d in θ = (m + ½ )1/λ

65. Ray optics is valid, when characteristic dimensions are

Of the order of one millimeter

Of the same order as the wavelength of light

Much smaller than the wavelength of length

Much larger than the wavelength of light

66. Appearance of colour in thin films is due to

Diffraction

Interference

Polarization

Dispersion

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

Sound

Supersonics

Ultrasonics

Light

68. 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

Two coherent light waves can be made to interfere

Light can be diffracted

Light can be polarized

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

Wave number

Wave front

Wave form

Wavelength

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

Comparable

None of these

Both

Not comparable

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

Wave front

A ray

A half-period zone

Vibrator

72. Which of the following has least wavelength?

γ-rays

X-rays

Ultra-violet rays

Cosmic-rays

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

Compton effect

Laue’s pattern

Bragg’s law

Huygen’s formula

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

Be close to each other

Of same amplitude

Have constant phase difference

Be narrow

75. Longitudinal waves do not exhibit

Reflection

Diffraction

Polarization

Refraction

Page 4 of 4

76. The blue colour of the sky is due to

Reflection

Diffraction

Polarization

Scattering

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

Refraction

Diffraction

Interference

Reflection

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

Same amplitude of vibration

Same wavelength

Same wave length with constant phase difference

Same amplitude and wavelength

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

16l

25l

80. Choose the correct statement

Rays may be normal to wave front

Rays are not normal to wave front

Rays are normal to wave front

There is no relationship between rays and wave fronts

81. Diffraction fringes are

Distance between them increases

They are adjacent with no space in between

Distance between then decreases

Equally spaced

82. The principle of Michelson’s interferometers is

Dispersion

Reflection

Refraction

Interference

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

Base

Origin

Producer

Source

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

Laser rays are not absorbed

Laser rays are most coherent waves

Laser rays are high velocity waves

Laser rays propagate in a straight line

85. 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 simple glass sheet

A Plano convex lens and the plane glass plate

None of these

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

An electromagnetic wave

A sound wave

A transverse waves

A longitudinal wave

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

Have a lower frequency

Cannot be polarized

Do not affect a photographic plate

Cannot be diffracted

88. In an interference pattern

Both dark and bright fringes are of equal width

Central fringes are brighter than the outer fringes

Dark fringes are wider than bright fringe

Bright fringes are wider than dark fringes

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Maan AliLast Updated: April 18, 2025

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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

agr is s tiyari krangay to hm uni test pas krlangy?

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

ECAT Physics Lights and Optics Online Test

Physics Lights and Optics MCQS Online Test

ECAT Physics Lights and Optics Chapter Online Test

Physics Lights and Optics Chapter Online Test

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