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

Wave front

Vibrator

A half-period zone

A ray

2. The cause of mirage observed in desert is

Total internal reflection

Scattering

Reflection

Refraction

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

16l

25l

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

Wave front

Wavelength

Wave form

Wave number

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

Y = (m + 1/2) λL/d

Y = (m + 1) λL/d

Y = (m + 1/2) λd/L

Y = (m + ½) dL/λ

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

Crest

Wavelength

Wave front

Trough

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

Band emission spectrum

Line absorption spectrum

Band absorption spectrum

Line emission spectrum

8. 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

Using monochromatic light of higher frequency

Increasing the distance between the slits

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

Both reflected and refracted light

Refracted light

Neither reflected nor refracted light

Reflected light

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

Fringe width

Intensity ratio of the sources

Wavelength

Distance between the slits

11. Which of the following has least wavelength?

Cosmic-rays

γ-rays

Ultra-violet rays

X-rays

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

Of nearly the same frequency

Of the same frequency and having definite phase relationship

Of same frequency

Different wavelength

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

Not comparable

Comparable

Both

None of these

14. Appearance of colour in thin films is due to

Polarization

Dispersion

Diffraction

Interference

15. 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

Interference pattern produced due to thin oil film

Total internal reflection of light

Polarization

16. Choose the correct statement

Rays are not normal to wave front

Rays may be normal to wave front

There is no relationship between rays and wave fronts

Rays are normal to wave front

17. In an interference pattern

Bright fringes are wider than dark fringes

Dark fringes are wider than bright fringe

Central fringes are brighter than the outer fringes

Both dark and bright fringes are of equal width

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

Increasing gradually

It is constant at the center

None of these

Decreasing gradually

19. 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

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

Electromagnetic

In the form of a narrow beam

Monochromatic

Incoherent

21. 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

22. Crystals of a material can behave as

Diffraction grating

Concave

Convex lens

Interferometer

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

Same amplitude of vibration

Same amplitude and wavelength

Same wavelength

Same wave length with constant phase difference

24. Diffraction fringes are

Distance between then decreases

Equally spaced

Distance between them increases

They are adjacent with no space in between

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

Diffraction

Interference

Refraction

Reflection

Page 2 of 4

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

d sin θ = (m + 1/2)λ

d in θ = (m + ½ )1/λ

d sin θ = (m + 1)λ

d sin θ = (m + 1/2)π/λ

27. The blue colour of the sky is due to

Scattering

Diffraction

Reflection

Polarization

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

Light can be polarized

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

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

Young

Newton

None of these

Huygen

30. Polarization occurs only in ________ waves

Matter waves

Transverse

Longitudinal

Mechanical waves

31. 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 10¹¹ to 5 x 10¹⁴ Hz

5 x 10⁵ to 5 x 10¹¹ Hz

5 x 10¹⁴ to 5 x 10¹⁷ Hz

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

Coinciding

Close together

Opposite to each other

At a far off distance

33. 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

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

2 x 10¯⁵ mm

5 x 10¯³ mm

2 x 10¯³ mm

500 mm

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

Momentum

Energy

Intensity

Amplitude

36. The idea of light as wave produced by

Michelson

Huygen

Newton

Thomos young

37. 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

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

None of these

Sound

Feeling

Vision

39. A polarizer is used to

Reduced intensity of light

Produce polarized light

Produce unpolarised light

Increase intensity of light

40. In a plane polarized light

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

No vibration at all

Vibration in all direction

Vibration in two mutually perpendicular directions

41. Can two head lights of car can produce interference

Partly produce interference

None of these

Yes

42. Longitudinal waves do not exhibit

Refraction

Diffraction

Reflection

Polarization

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

An elliptical wave front

A cylindrical wave front

A spherical wave front

A plane wave front

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

Laser rays propagate in a straight line

Laser rays are high velocity waves

Laser rays are most coherent waves

Laser rays are not absorbed

45. Which one of the following cannot be polarized?

Radio waves

X-rays

Ultraviolet rays

Sound waves

46. 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

47. For constructive interference the path difference is

Mλ

(m – 1)λ

½ mλ

m²λ

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

Diffraction

Reflection

Refraction

Origin of spectra

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

Interference

Diffraction

None of these

Doppler’s effect

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

Different width

Equal width

None of these

Dark fringes are thicker than bright

Page 3 of 4

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

Electromagnetic

Monochromatic

In the form of a narrow beam

Incoherent

52. 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

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

Base

Source

Origin

Producer

54. 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

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

Diffraction

Origin of spectra

Reflection

Refraction

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

None of these

Minimum

Maximum

Zero

57. Wavelength of light of frequency 100 Hz is

2 x 10⁶ m

5 x 10⁶ m

4 x 10⁶ m

3 x 10⁶ m

58. 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 bright bands

Interference in which breadth of the fringe will be slightly increase

Interference with dark bands

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

Transmission

Polarization

Absorption

Diffraction

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

Diffraction

Reflection

Transmission

Refraction

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

All of these

Phase

Wavelength

Frequency

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

All of these

Emission spectrum

Continuous emission spectrum

Line spectrum

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

None of these

Source

Source of secondary wave front

Source of wave front

64. 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

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

Interference of light

Reflection of light

Diffraction of light

None of these

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

Parabolic

Elliptical

Circular

Straight

67. Light on passing through a Polaroid is

Elliptically polarized

Plane polarized

Un-polarized

Circularly polarized

68. The principle of Michelson’s interferometers is

Refraction

Reflection

Interference

Dispersion

69. 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

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

Polarization

Diffraction

Interference

Reflection

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

Polarization

Destructive interference

Constructive interference

Diffraction

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

Huygen’s formula

Compton effect

Bragg’s law

Laue’s pattern

73. The fringe spacing in case of blue light

None of these

Remains the same

Increases

Decrease

74. Ray optics is valid, when characteristic dimensions are

Of the same order as the wavelength of light

Much larger than the wavelength of light

Much smaller than the wavelength of length

Of the order of one millimeter

75. Diffraction effect is

Less for a round edge

More for a sharp edge

Less for a sharp edge

More for a round edge

Page 4 of 4

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

d sin θ = m/2 λ

d sin θ = mλ

d sin θ = 2λm

md cos θ = λ

77. 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 less than the wave

Speed of propagation of the wave

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

Sound

Light

Ultrasonics

Supersonics

79. Huygen’s wave theory of light cannot explain

Photoelectric effect

Interference

Diffraction

Polarization

80. A spherical wave front is that which has

A point source

A source

A extended source

None of these

81. Central spot of New tons rings

Dart for large wavelength

Bright for large wavelength

Bright

Dark

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

Have constant phase difference

Of same amplitude

Be narrow

Be close to each other

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

3 x 10⁵ ms¯¹

3 x 10¯¹⁰ ms¯¹

3 x 10⁸ ms¯¹

3.1 x 10⁸ ms¯¹

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

?/3

?/4

?/2

?/6

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

d Sin θ = (m + 1/2)λ

2π Sin θ = (m + 1/2)λ

½ d Sin θ = mλ

m Sin θ = (d + 1/2)λ

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

Plano-convex

Convexo-concave

Double-convex

Plano-concave

87. Huygen’s wave theory of light cannot explain

Photoelectric effect

Diffraction

Polarization

Interference

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

A sound wave

An electromagnetic wave

A longitudinal wave

A transverse waves

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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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