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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. 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

2. The principle of Michelson’s interferometers is

Dispersion

Refraction

Reflection

Interference

3. Crystals of a material can behave as

Diffraction grating

Convex lens

Interferometer

Concave

4. 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

Integral multiple of λ/2

Even integral multiple of λ

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

Frequency

Phase

Wavelength

All of these

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

Crest

Wave front

Trough

Wavelength

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

Diffraction

Doppler’s effect

None of these

Interference

8. A polarizer is used to

Increase intensity of light

Produce unpolarised light

Reduced intensity of light

Produce polarized light

9. 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

10. The idea of light as wave produced by

Michelson

Huygen

Newton

Thomos young

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

A ray

Vibrator

A half-period zone

Wave front

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

Y = (m + 1) λL/d

Y = (m + 1/2) λL/d

Y = (m + 1/2) λd/L

Y = (m + ½) dL/λ

13. Light appears to travel in straight lies since

Its velocity is very large

Its wavelength is very small

It is not absorbed by the atmosphere

It is reflected by the atmosphere

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

Decreasing gradually

It is constant at the center

None of these

Increasing gradually

15. 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 10¹¹ to 5 x 10¹⁴ Hz

5 x 10⁵ to 5 x 10⁵ Hz

5 x 10⁵ to 5 x 10¹¹ Hz

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

d Sin θ = (m + 1/2)λ

½ d Sin θ = mλ

2π Sin θ = (m + 1/2)λ

m Sin θ = (d + 1/2)λ

17. 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

Increasing the distance between the slits

Using monochromatic light of longer wavelength

Decreasing the distance between the screen and the slits

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

Interference with bright bands

19. Diffraction fringes are

Distance between then decreases

Distance between them increases

They are adjacent with no space in between

Equally spaced

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

Wavelength

Wave form

Wave number

Wave front

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

Energy

Amplitude

Intensity

Momentum

22. 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

23. Longitudinal waves do not exhibit

Polarization

Diffraction

Refraction

Reflection

24. 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 = 2π dm

λ = dm

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

Impossible to predict

No interference fringes will be seen

Alternate dark and bright fringes will be seen

Colored fringes will be seen

Page 2 of 4

26. The blue colour of the sky is due to

Scattering

Reflection

Polarization

Diffraction

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

Diffraction

Absorption

Transmission

Polarization

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

A sound wave

A transverse waves

A longitudinal wave

An electromagnetic wave

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

Transmission

Diffraction

Reflection

Refraction

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

Sound

None of these

Vision

Feeling

31. 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

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

Zero

None of these

Minimum

Maximum

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

Laser rays are not absorbed

Laser rays are high velocity waves

Laser rays are most coherent waves

Laser rays propagate in a straight line

34. 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 + 1/2)λ

d sin θ = (m + 1)λ

35. 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

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

Distance between the slits

Intensity ratio of the sources

Fringe width

Wavelength

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

Incoherent

Electromagnetic

Monochromatic

In the form of a narrow beam

38. The fringe spacing in case of blue light

Decrease

Remains the same

None of these

Increases

39. In a plane polarized light

No vibration at all

Vibration in two mutually perpendicular directions

Vibration in all direction

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

40. Diffraction effect is

More for a round edge

Less for a sharp edge

More for a sharp edge

Less for a round edge

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

Polarization

Interference

Reflection

Diffraction

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

Destructive interference

Constructive interference

Polarization

Diffraction

43. Polarization occurs only in ________ waves

Mechanical waves

Transverse

Matter waves

Longitudinal

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

?/4

?/2

?/3

?/6

45. Wavelength of light of frequency 100 Hz is

2 x 10⁶ m

3 x 10⁶ m

4 x 10⁶ m

5 x 10⁶ m

46. 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

47. Light on passing through a Polaroid is

Circularly polarized

Elliptically polarized

Un-polarized

Plane polarized

48. Which of the following has least wavelength?

Ultra-violet rays

X-rays

Cosmic-rays

γ-rays

49. Which one of the following cannot be polarized?

X-rays

Sound waves

Ultraviolet rays

Radio waves

50. For constructive interference the path difference is

½ mλ

(m – 1)λ

Mλ

m²λ

Page 3 of 4

51. Huygen’s wave theory of light cannot explain

Polarization

Photoelectric effect

Diffraction

Interference

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

Band absorption spectrum

Band emission spectrum

Line emission spectrum

Line absorption spectrum

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

Plano-convex

Convexo-concave

Double-convex

Plano-concave

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

Circular

Straight

Elliptical

Parabolic

55. 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

56. 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

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

Speed of propagation less than the wave

Speed of propagation greater than wave

B and C

Speed of propagation of the wave

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

Energy of different colors is different

Velocity of different colors is different

Amplitude of different colors is different

Phase of different colors is different

59. The setting of Newton’s rings is

A Plano convex lens and simple glass sheet

None of these

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

A Plano convex lens and the plane glass plate

60. Huygen’s wave theory of light cannot explain

Interference

Photoelectric effect

Polarization

Diffraction

61. Appearance of colour in thin films is due to

Diffraction

Interference

Dispersion

Polarization

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

16l

25l

63. 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

64. 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

65. The cause of mirage observed in desert is

Refraction

Scattering

Total internal reflection

Reflection

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

Laue’s pattern

Huygen’s formula

Compton effect

Bragg’s law

67. 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 = 2λm

md cos θ = λ

d sin θ = mλ

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

Young

Newton

None of these

Huygen

69. 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

Light can be polarized

Two coherent light waves can be made to interfere

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

Origin of spectra

Reflection

Refraction

Diffraction

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

Comparable

Both

Not comparable

None of these

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

In the form of a narrow beam

Electromagnetic

Incoherent

Monochromatic

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

A cylindrical wave front

A plane wave front

An elliptical wave front

A spherical wave front

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

Light

Sound

Supersonics

Ultrasonics

75. 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

Page 4 of 4

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

Same amplitude and wavelength

Same wavelength

Same wave length with constant phase difference

Same amplitude of vibration

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

Line spectrum

Emission spectrum

Continuous emission spectrum

All of these

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

Cannot be polarized

Have a lower frequency

Cannot be diffracted

Do not affect a photographic plate

79. 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

Total internal reflection of light

Diffraction pattern

80. A spherical wave front is that which has

None of these

A point source

A extended source

A source

81. Can two head lights of car can produce interference

Partly produce interference

None of these

Yes

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

Source

Producer

Base

Origin

83. 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

84. Ray optics is valid, when characteristic dimensions are

Much smaller than the wavelength of length

Of the same order as the wavelength of light

Of the order of one millimeter

Much larger than the wavelength of light

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

Source

None of these

Source of secondary wave front

Source of wave front

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

Refraction

Origin of spectra

Diffraction

Reflection

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

Diffraction

Refraction

Reflection

Interference

88. Central spot of New tons rings

Dart for large wavelength

Bright for large wavelength

Dark

Bright

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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

Agr koi Matric(9th+10th) and Fsc(11th+12th) and Ecat+Mcat k complete video lectures lena chahta h tou in nums pe contact kar

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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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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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