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

Y = (m + 1/2) λd/L

Y = (m + ½) dL/λ

Y = (m + 1) λL/d

Y = (m + 1/2) λL/d

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

A ray

Wave front

A half-period zone

Vibrator

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

Decreasing gradually

Increasing gradually

None of these

It is constant at the center

4. Which one of the following cannot be polarized?

Sound waves

X-rays

Ultraviolet rays

Radio waves

5. The idea of light as wave produced by

Huygen

Thomos young

Michelson

Newton

6. The fringe spacing in case of blue light

Decrease

None of these

Increases

Remains the same

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

Interference

Diffraction

Polarization

Reflection

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

Source

Origin

Producer

Base

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

Double-convex

Plano-concave

Plano-convex

Convexo-concave

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

d sin θ = 2λm

d sin θ = mλ

md cos θ = λ

d sin θ = m/2 λ

11. 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

Interference with dark bands

Interference with bright bands

No interference

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

3.1 x 10⁸ ms¯¹

3 x 10⁸ ms¯¹

3 x 10⁵ ms¯¹

3 x 10¯¹⁰ ms¯¹

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

Wavelength

Wave number

Wave form

Wave front

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

Refraction

Diffraction

Reflection

Interference

15. Central spot of New tons rings

Dark

Dart for large wavelength

Bright for large wavelength

Bright

16. Appearance of colour in thin films is due to

Interference

Dispersion

Polarization

Diffraction

17. The blue colour of the sky is due to

Scattering

Polarization

Reflection

Diffraction

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

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

Two coherent light waves can be made to interfere

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

Refraction

Transmission

Diffraction

Reflection

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

16l

25l

21. Ray optics is valid, when characteristic dimensions are

Of the same order as the wavelength of light

Much smaller than the wavelength of length

Much larger than the wavelength of light

Of the order of one millimeter

22. 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

23. Polarization occurs only in ________ waves

Longitudinal

Matter waves

Transverse

Mechanical waves

24. 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

Diffraction pattern

Interference pattern produced due to thin oil film

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

All of these

Frequency

Phase

Wavelength

Page 2 of 4

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

Origin of spectra

Refraction

Reflection

Diffraction

27. The principle of Michelson’s interferometers is

Reflection

Dispersion

Interference

Refraction

28. 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

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

Reflected light

Neither reflected nor refracted light

Both reflected and refracted light

Refracted light

30. Light appears to travel in straight lies since

Its velocity is very large

It is not absorbed by the atmosphere

It is reflected by the atmosphere

Its wavelength is very small

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

?/2

?/6

?/4

?/3

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

2π Sin θ = (m + 1/2)λ

d Sin θ = (m + 1/2)λ

½ d Sin θ = mλ

m Sin θ = (d + 1/2)λ

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

Wavelength

Distance between the slits

Intensity ratio of the sources

Fringe width

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

Supersonics

Sound

Light

Ultrasonics

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

Of same frequency

Of nearly the same frequency

Different wavelength

Of the same frequency and having definite phase relationship

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

None of these

Comparable

Not comparable

Both

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

Intensity

Momentum

Energy

Amplitude

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

Electromagnetic

Monochromatic

Incoherent

In the form of a narrow beam

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

Monochromatic

Electromagnetic

In the form of a narrow beam

Incoherent

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

Odd integral multiple of λ/2

Integral multiple of λ/2

Even integral multiple of λ

Integral multiple of λ

41. Diffraction fringes are

Distance between them increases

Equally spaced

Distance between then decreases

They are adjacent with no space in between

42. 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 polarized

Light can be diffracted

43. 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

5 x 10¯³ mm

2 x 10¯⁵ mm

44. Huygen’s wave theory of light cannot explain

Diffraction

Polarization

Interference

Photoelectric effect

45. 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

Polarization

Total internal reflection of light

46. In a plane polarized light

Vibration in all direction

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

Vibration in two mutually perpendicular directions

No vibration at all

47. 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

B and C

Speed of propagation less than the wave

48. 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?

Increasing the distance between the slits

Decreasing the distance between the screen and the slits

Using monochromatic light of higher frequency

Using monochromatic light of longer wavelength

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

Have a lower frequency

Do not affect a photographic plate

Cannot be diffracted

Cannot be polarized

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

Destructive interference

Polarization

Diffraction

Constructive interference

Page 3 of 4

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

Wavelength

Crest

Trough

Wave front

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

Continuous emission spectrum

All of these

Line spectrum

Emission spectrum

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

Diffraction

None of these

Doppler’s effect

Interference

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

None of these

Maximum

Minimum

Zero

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

Vision

Sound

Feeling

None of these

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

Young

Newton

None of these

Huygen

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

Transmission

Diffraction

Polarization

Absorption

58. The setting of Newton’s rings is

None of these

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

59. A polarizer is used to

Reduced intensity of light

Produce unpolarised light

Produce polarized light

Increase intensity of light

60. Wavelength of light of frequency 100 Hz is

4 x 10⁶ m

3 x 10⁶ m

2 x 10⁶ m

5 x 10⁶ m

61. For constructive interference the path difference is

m²λ

Mλ

(m – 1)λ

½ mλ

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

Equal width

Dark fringes are thicker than bright

Different width

None of these

63. Crystals of a material can behave as

Convex lens

Diffraction grating

Interferometer

Concave

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

Bragg’s law

Huygen’s formula

Compton effect

Laue’s pattern

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

Opposite to each other

Coinciding

At a far off distance

Close together

66. Longitudinal waves do not exhibit

Refraction

Polarization

Diffraction

Reflection

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

Same wave length with constant phase difference

Same amplitude of vibration

Same wavelength

Same amplitude and wavelength

68. A spherical wave front is that which has

None of these

A source

A point source

A extended source

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

Straight

Circular

Elliptical

Parabolic

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

A transverse waves

A longitudinal wave

An electromagnetic wave

A sound wave

71. Light on passing through a Polaroid is

Un-polarized

Circularly polarized

Plane polarized

Elliptically polarized

72. Huygen’s wave theory of light cannot explain

Diffraction

Photoelectric effect

Polarization

Interference

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

Origin of spectra

Diffraction

Refraction

Reflection

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

Source

None of these

Source of wave front

Source of secondary wave front

75. Diffraction effect is

Less for a round edge

More for a sharp edge

More for a round edge

Less for a sharp edge

Page 4 of 4

76. In an interference pattern

Dark fringes are wider than bright fringe

Central fringes are brighter than the outer fringes

Bright fringes are wider than dark fringes

Both dark and bright fringes are of equal width

77. Can two head lights of car can produce interference

None of these

Partly produce interference

Yes

78. Choose the correct statement

There is no relationship between rays and wave fronts

Rays are not normal to wave front

Rays may be normal to wave front

Rays are normal to wave front

79. The cause of mirage observed in desert is

Scattering

Reflection

Total internal reflection

Refraction

80. 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

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

Be close to each other

Have constant phase difference

Of same amplitude

Be narrow

82. 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

λ = 2π dm

2λ = dm

λ = dm

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

Band emission spectrum

Band absorption spectrum

Line emission spectrum

Line absorption spectrum

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

Alternate dark and bright fringes will be seen

Impossible to predict

Colored fringes will be seen

No interference fringes will be seen

85. 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 10¹¹ to 5 x 10¹⁴ Hz

5 x 10⁵ to 5 x 10¹¹ Hz

5 x 10⁵ to 5 x 10⁵ Hz

5 x 10¹⁴ to 5 x 10¹⁷ Hz

86. Which of the following has least wavelength?

γ-rays

Ultra-violet rays

X-rays

Cosmic-rays

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

Amplitude of different colors is different

Energy of different colors is different

Velocity of different colors is different

Phase of different colors is different

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

d sin θ = (m + 1/2)π/λ

d in θ = (m + ½ )1/λ

d sin θ = (m + 1)λ

d sin θ = (m + 1/2)λ

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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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