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General Science Quiz: Interference, Diffraction and Polarisation of Light

  • 11 questions
  • 11 minutes
  • Difficulty: Medium
Useful for:SSCSSC CGLSSC CHSLUPSC Civil ServicesRRB NTPCRRB ALPRRB JEState ExamsNDA
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About this quiz

This General Science quiz on Interference, Diffraction and Polarisation of Light puts 11 multiple-choice questions to you, the verified MCQs published with GK24's note on the topic, 3 of them asked in real previous-year papers. Every question carries a full explanation of why the correct option is right and why the other options are wrong, so you learn the fact behind the answer rather than the letter. Attempt it right after reading the note, keep to the timer, and use the explanations at the end to mark what needs another look. Sit it again before the exam as a quick revision of the topic.

Questions in this quiz

11 questions with answers and explanations

Q1.General ScienceAsked in: Rajasthan · RSMSSB Lab Assistant 2018 Official PaperMedium

Brewster's law is (where the symbol mu stands for the refractive index and i_p for the polarising angle)

  1. A.i_p = 90 degrees
  2. B.mu = tan i_p
  3. C.i_p minus r = tan mu
  4. D.i_p = tan mu
Show answer
Correct answer: B. mu = tan i_p

Brewster found that when unpolarised light falls on a transparent surface at one particular angle of incidence, called the polarising angle, the reflected light is completely plane polarised, and at that angle the refractive index of the surface equals the tangent of the polarising angle.

Q2.General ScienceAsked in: Rajasthan · 09 Sept, 2025Hard

The headlights of a distant car are 1.4 m apart. If the diameter of the pupil of the eye is 3 mm, what is the maximum distance at which the two headlights can be resolved? Consider the headlights as point sources of wavelength 500 nm.

  1. A.3448 m
  2. B.68.96 m
  3. C.34.48 m
  4. D.6896 m
Show answer
Correct answer: D. 6896 m

By the Rayleigh criterion the smallest angle the eye can resolve is 1.22 times the wavelength divided by the diameter of the pupil, that is 1.22 multiplied by 500 nanometres and divided by 3 millimetres, which comes to about 2.03 times ten to the power minus four radian.

Q3.General ScienceAsked in: Uttar Pradesh · UPPSC GIC Lecturer Physics 2021Hard

When a thin glass plate of refractive index 1.5 is introduced in one of the arms of a Michelson interferometer using light of wavelength 5890 angstrom, there is a shift of 10 fringes. The thickness of the plate is

  1. A.5.89 m
  2. B.5.89 times ten to the power minus three metre
  3. C.5.89 times ten to the power minus six metre
  4. D.5.89 times ten to the power minus four metre
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Correct answer: C. 5.89 times ten to the power minus six metre

Inserting a plate of thickness t in one arm makes the light cross it twice, so the extra path introduced is twice the thickness times the quantity refractive index minus one.

Q5.General ScienceEasy

The brilliant colours seen in a soap bubble or in a thin film of oil spread on water are caused by

  1. A.Interference of light reflected from the two surfaces of the film
  2. B.Total internal reflection inside the film
  3. C.Dispersion of light as in a prism
  4. D.Scattering of light by the molecules of the film
Show answer
Correct answer: A. Interference of light reflected from the two surfaces of the film

The light reflected from the upper surface of the thin film and the light reflected from the lower surface travel slightly different distances and interfere.

Q6.General ScienceMedium

In Young's double slit experiment the width of a fringe will increase if

  1. A.The screen is moved closer to the slits
  2. B.The separation between the slits is reduced
  3. C.Blue light replaces red light
  4. D.The slits are made narrower without changing their separation
Show answer
Correct answer: B. The separation between the slits is reduced

The fringe width equals the wavelength multiplied by the distance of the screen and divided by the separation of the two slits.

Q8.General ScienceMedium

A person standing in a room can hear someone speaking in the next room through an open door but cannot see the speaker. The reason is that

  1. A.Sound travels faster than light
  2. B.The wavelength of sound is comparable with the width of the door, so sound diffracts strongly
  3. C.Sound is a transverse wave and light is longitudinal
  4. D.Light is absorbed by the air while sound is not
Show answer
Correct answer: B. The wavelength of sound is comparable with the width of the door, so sound diffracts strongly

Diffraction, the bending of a wave round an edge, is appreciable only when the obstacle or opening is of the same order of size as the wavelength.

Q9.General ScienceMedium

The resolving power of an astronomical telescope can be increased by

  1. A.Increasing the diameter of the objective lens
  2. B.Increasing the focal length of the eyepiece
  3. C.Using light of longer wavelength
  4. D.Decreasing the diameter of the objective lens
Show answer
Correct answer: A. Increasing the diameter of the objective lens

The smallest angular separation a telescope can resolve is 1.22 times the wavelength divided by the diameter of the objective, so a larger aperture means a smaller limit of resolution and a greater resolving power.

Q11.General ScienceEasy

Young's famous double slit experiment, performed in 1801, established that light

  1. A.Consists of material particles
  2. B.Shows interference and therefore behaves as a wave
  3. C.Travels faster in water than in air
  4. D.Is composed of seven colours
Show answer
Correct answer: B. Shows interference and therefore behaves as a wave

Thomas Young passed light from one source through two narrow slits placed close together and obtained alternate bright and dark bands on a screen.

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