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WBJEE Wave Optics — practice questions

Explore 75 free Wave Optics questions in WBJEE Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Wave Optics questions and exercises with answers

Showing questions 1–30 of 75.

Two light sources can produce sustained interference fringes on a screen only if they are:Read the answer and worked solution →**Huygens' principle** states that every point on a wavefront acts as a:Read the answer and worked solution →Which of the following phenomena conclusively proves that **light is a transverse wave**?Read the answer and worked solution →When light passes from one medium to another, which property remains **unchanged**?Read the answer and worked solution →The **wavelength** of light of wavelength 600 nm in air becomes (in water, n = 1.33) approximately:Read the answer and worked solution →When unpolarized light passes through a single ideal polarizer, the transmitted intensity is:Read the answer and worked solution →**Malus' law** gives the transmitted intensity through a second polarizer as:Read the answer and worked solution →In Young's double-slit experiment, the fringe width $w$ is given by:Read the answer and worked solution →In Young's experiment, if the entire setup is immersed in a medium of refractive index $n$, the fringe width:Read the answer and worked solution →Two slits 0.5 mm apart are illuminated with light of 600 nm. The fringes are observed on a screen 1 m away. The fringe width is:Read the answer and worked solution →Light of intensity $I_0$ passes through two polarizers whose axes make 60° with each other. The transmitted intensity is:Read the answer and worked solution →Brewster's angle for light going from air (n=1) to glass (n=1.5) is approximately:Read the answer and worked solution →In a single-slit Fraunhofer diffraction pattern, the first minimum occurs at angle $\theta$ satisfying:Read the answer and worked solution →A telescope objective has diameter 2.5 m. Its angular resolution at $\lambda = 5500$ Å is approximately:Read the answer and worked solution →White light (400–700 nm) passes through a glass of refractive index 1.55. The wavelength range observed in the glass becomes approximately:Read the answer and worked solution →The optical path of a 3 cm ray in flint glass (n = 1.6) equals that of an unknown medium (n = 1.25) over distance $x$. Then $x$ is:Read the answer and worked solution →Light enters a glass slab (n = 1.5) at angle i = 30°. The angle of refraction r inside glass is approximately:Read the answer and worked solution →For two equal-amplitude coherent sources, the maximum and minimum intensities are:Read the answer and worked solution →Two crossed polaroids transmit light of intensity:Read the answer and worked solution →The refractive index of glass is 1.5. The speed of light in glass is:Read the answer and worked solution →Snell's law states that the ratio sin(i)/sin(r) for two media is:Read the answer and worked solution →The wavefront from a point source is:Read the answer and worked solution →Young's double-slit experiment demonstrates which phenomenon?Read the answer and worked solution →Two waves with the same frequency and constant phase difference are called:Read the answer and worked solution →In Young's double-slit experiment, the bright fringe condition is path difference equals:Read the answer and worked solution →Polarization of light is possible because light is:Read the answer and worked solution →In Young's experiment, fringe width β equals:Read the answer and worked solution →In Young's experiment with d = 1 mm, D = 1 m, light wavelength 600 nm, fringe width is:Read the answer and worked solution →When light goes from a less dense to denser medium (e.g., air to water), it bends:Read the answer and worked solution →Critical angle for total internal reflection from water (n = 4/3) to air:Read the answer and worked solution →

Worked practice questions

Two light sources can produce sustained interference fringes on a screen only if they are:

  1. Coherent (constant phase difference)
  2. Of identical intensity
  3. From the same physical lamp
  4. Polarised in the same direction
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Correct answer: A. Coherent (constant phase difference)

Sustained interference needs sources with a constant phase relationship over time, which is what coherence means. Two ordinary lamps emit light with phases that vary randomly at $10^{-8}$ s scale so their interference pattern washes out almost instantly. The two slits in Young's experiment achieve coherence because both are illuminated by the same primary source, inheriting its phase. Equal intensity (B) improves fringe contrast but is not required. Same lamp (C) is one way to ensure coherence but not the only way (e.g. laser pairs). Polarisation alignment (D) matters for contrast, not for the existence of fringes.

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**Huygens' principle** states that every point on a wavefront acts as a:

  1. Source of plane waves only
  2. Secondary source emitting wavelets in all directions
  3. Absorber of waves
  4. Source of longitudinal waves only
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Correct answer: B. Secondary source emitting wavelets in all directions

Each point on a wavefront becomes a secondary source of spherical wavelets. The new wavefront at a later time is the **envelope** of these wavelets in the forward direction (backward wavelets are taken as ineffective).

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Which of the following phenomena conclusively proves that **light is a transverse wave**?

  1. Reflection
  2. Refraction
  3. Interference
  4. Polarization
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Correct answer: D. Polarization

Only transverse waves can be polarized (oscillations restricted to one plane perpendicular to propagation). Reflection, refraction and interference occur for longitudinal waves too — they don't distinguish wave type.

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