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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. Crystals of a material can behave as

Interferometer

Concave

Convex lens

Diffraction grating

2. 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

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

Coinciding

Close together

At a far off distance

Opposite to each other

4. Central spot of New tons rings

Bright

Dark

Dart for large wavelength

Bright for large wavelength

5. Appearance of colour in thin films is due to

Diffraction

Polarization

Dispersion

Interference

6. The idea of light as wave produced by

Thomos young

Newton

Michelson

Huygen

7. 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

Decreasing gradually

Increasing gradually

None of these

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

Line emission spectrum

Band absorption spectrum

Band emission spectrum

Line absorption spectrum

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

Vibrator

A ray

Wave front

A half-period zone

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

Diffraction

Transmission

Reflection

Refraction

11. Light appears to travel in straight lies since

Its wavelength is very small

It is not absorbed by the atmosphere

Its velocity is very large

It is reflected by the atmosphere

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

3 x 10⁸ ms¯¹

3 x 10¯¹⁰ ms¯¹

3 x 10⁵ ms¯¹

3.1 x 10⁸ ms¯¹

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

Doppler’s effect

Diffraction

Interference

None of these

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

Diffraction of light

Interference of light

Reflection of light

None of these

15. Huygen’s wave theory of light cannot explain

Diffraction

Polarization

Interference

Photoelectric effect

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

Cannot be polarized

Cannot be diffracted

Do not affect a photographic plate

Have a lower frequency

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

Feeling

None of these

Sound

Vision

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

?/6

?/4

?/3

?/2

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

B and C

Speed of propagation greater than wave

Speed of propagation of the wave

Speed of propagation less than the wave

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

In the form of a narrow beam

Monochromatic

Incoherent

Electromagnetic

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

An elliptical wave front

A cylindrical wave front

A plane wave front

A spherical wave front

22. Diffraction fringes are

Distance between then decreases

They are adjacent with no space in between

Distance between them increases

Equally spaced

23. 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 dark bands

Interference with bright bands

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

Neither reflected nor refracted light

Both reflected and refracted light

Refracted light

Reflected light

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

Wave front

Trough

Wavelength

Crest

Page 2 of 4

26. 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

Interference pattern produced due to thin oil film

Diffraction pattern

Total internal reflection of light

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

Fringe width

Intensity ratio of the sources

Wavelength

Distance between the slits

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

Source of secondary wave front

None of these

Source

Source of wave front

29. Which one of the following cannot be polarized?

Ultraviolet rays

X-rays

Sound waves

Radio waves

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

Momentum

Amplitude

Intensity

Energy

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

None of these

Not comparable

Comparable

Both

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

Laser rays propagate in a straight line

Laser rays are not absorbed

Laser rays are most coherent waves

Laser rays are high velocity waves

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

A sound wave

A longitudinal wave

A transverse waves

An electromagnetic wave

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

Origin of spectra

Diffraction

Reflection

Refraction

35. For constructive interference the path difference is

m²λ

Mλ

(m – 1)λ

½ mλ

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

Polarization

Interference

Diffraction

Reflection

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

½ d Sin θ = mλ

m Sin θ = (d + 1/2)λ

2π Sin θ = (m + 1/2)λ

d Sin θ = (m + 1/2)λ

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

2 x 10¯³ mm

500 mm

2 x 10¯⁵ mm

5 x 10¯³ mm

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

Ultrasonics

Light

Sound

Supersonics

40. Huygen’s wave theory of light cannot explain

Polarization

Diffraction

Photoelectric effect

Interference

41. 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 10¹¹ to 5 x 10¹⁴ Hz

5 x 10⁵ to 5 x 10⁵ Hz

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

Of same frequency

Of the same frequency and having definite phase relationship

Different wavelength

Of nearly the same frequency

43. The blue colour of the sky is due to

Polarization

Diffraction

Scattering

Reflection

44. A spherical wave front is that which has

A point source

A extended source

None of these

A source

45. 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

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

d sin θ = 2λm

d sin θ = m/2 λ

md cos θ = λ

d sin θ = mλ

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

No interference fringes will be seen

Alternate dark and bright fringes will be seen

Impossible to predict

Colored fringes will be seen

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

Polarization

Destructive interference

Constructive interference

Diffraction

49. Longitudinal waves do not exhibit

Reflection

Refraction

Diffraction

Polarization

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

Compton effect

Bragg’s law

Laue’s pattern

Huygen’s formula

Page 3 of 4

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

Wave form

Wave front

Wavelength

Wave number

52. In a plane polarized light

Vibration in all direction

Vibration in two mutually perpendicular directions

No vibration at all

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

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

Same amplitude of vibration

Same amplitude and wavelength

Same wave length with constant phase difference

Same wavelength

54. Wavelength of light of frequency 100 Hz is

2 x 10⁶ m

3 x 10⁶ m

4 x 10⁶ m

5 x 10⁶ m

55. Choose the correct statement

Rays are normal to wave front

Rays are not normal to wave front

Rays may be normal to wave front

There is no relationship between rays and wave fronts

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

d in θ = (m + ½ )1/λ

d sin θ = (m + 1/2)π/λ

d sin θ = (m + 1)λ

d sin θ = (m + 1/2)λ

57. Diffraction effect is

More for a sharp edge

Less for a round edge

More for a round edge

Less for a sharp edge

58. The principle of Michelson’s interferometers is

Reflection

Interference

Dispersion

Refraction

59. In an interference pattern

Central fringes are brighter than the outer fringes

Both dark and bright fringes are of equal width

Bright fringes are wider than dark fringes

Dark fringes are wider than bright fringe

60. The cause of mirage observed in desert is

Total internal reflection

Scattering

Refraction

Reflection

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

Y = (m + 1/2) λd/L

Y = (m + 1) λL/d

Y = (m + 1/2) λL/d

Y = (m + ½) dL/λ

62. 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 = dm

2λ = dm

λ = 2d/m

λ = 2π dm

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

Dark fringes are thicker than bright

Different width

Equal width

None of these

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

Light can be diffracted

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 polarized

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

Circular

Straight

Parabolic

Elliptical

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

Reflection

Refraction

Diffraction

Origin of spectra

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

Plano-convex

Double-convex

Convexo-concave

Plano-concave

68. 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

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

Diffraction

Absorption

Polarization

Transmission

70. A polarizer is used to

Reduced intensity of light

Produce polarized light

Increase intensity of light

Produce unpolarised light

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

In the form of a narrow beam

Incoherent

Monochromatic

Electromagnetic

72. 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

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

16l

25l

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

Phase of different colors is different

Energy of different colors is different

Amplitude of different colors is different

Velocity of different colors is different

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

All of these

Emission spectrum

Continuous emission spectrum

Line spectrum

Page 4 of 4

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

Producer

Origin

Base

Source

77. Light on passing through a Polaroid is

Elliptically polarized

Un-polarized

Circularly polarized

Plane polarized

78. Polarization occurs only in ________ waves

Mechanical waves

Transverse

Matter waves

Longitudinal

79. Which of the following has least wavelength?

γ-rays

X-rays

Ultra-violet rays

Cosmic-rays

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

Phase

Frequency

All of these

Wavelength

81. 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

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

Be close to each other

Of same amplitude

Be narrow

Have constant phase difference

83. Can two head lights of car can produce interference

None of these

Partly produce interference

Yes

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

Diffraction

Reflection

Refraction

Interference

85. The fringe spacing in case of blue light

Increases

None of these

Decrease

Remains the same

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

Light can be diffracted

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 polarized

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

None of these

Young

Huygen

Newton

88. Ray optics is valid, when characteristic dimensions are

Of the order of one millimeter

Much larger than the wavelength of light

Much smaller than the wavelength of length

Of the same order as the wavelength of light

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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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