NEET Wave Optics PYQs & Practice Questions

10 free NEET Physics questions on Wave Optics, starting with previous year questions (2016–2026). Tap “Show answer” to check each one. No login needed.

Topics: Huygens' Principle · Young's Double Slit Experiment · Diffraction · Polarisation · Interference and Coherence · Brewster's Angle / Polarization · Polarization - Malus's Law · Coherence Requirement for Interference · Young's Double Slit Experiment with White Light · Polarisation at Brewster's Angle · Young's Double Slit Experiment - Fringe Angular Separation · Single Slit Diffraction

Q1NEET 2026Intensity vs path difference
In Young's double-slit experiment, using monochromatic light of wavelength λ, the intensity of light at a point on the screen where the path difference is λ, is K units. The intensity of light at a point where the path difference is λ/3 will be:
- A. K
- B. 2K
- C. K/2
- D. K/4
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Answer: C — K/2
I=Imax cos²(Δφ/2). At path diff λ (Δφ=2π), I=K=Imax. At λ/3 (Δφ=2π/3), I=Imax cos²(π/3)=Imax/4=K/4.
Q2NEET 2026Energy conservation in interference/diffraction
In interference and diffraction, the light energy is redistributed. A. As there is no gain or loss of energy, these phenomena are consistent with the principle of conservation of energy. B. Diffraction and interference are characteristics exhibited only by light waves.
- A. A is false, but B is true
- B. A is true, but B is false
- C. A is true and B is also true
- D. Both A and B are false
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Answer: A — A is false, but B is true
A is true (energy conserved, redistributed). B is false — diffraction/interference occur in all waves, not just light.
Q3NEET 2026Deviation by a prism
A ray of monochromatic light is passing through an equilateral prism (ABC) as shown in the figure. The refracted ray (QR) is parallel to its base (BC) and the angle of incidence (i) is 50°. Then the angle of deviation (δ) is:
- A. 45°
- B. 55°
- C. 35°
- D. 40°
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Answer: C — 35°
For a ray refracted parallel to the base in an equilateral prism, deviation δ=2i-A=2(50)-60=40°.
Q4NEET 2025Brewster's Angle / Polarization
An unpolarized light beam travelling in air is incident on a medium of refractive index 1.73 at Brewster's angle. Then -
- A. reflected light is completely polarized and the angle of reflection is close to 60°
- B. reflected light is partially polarized and the angle of reflection is close to 30°
- C. both reflected and transmitted light are perfectly polarized with angles of reflection and refraction close to 60° and 30°, respectively
- D. transmitted light is completely polarized with angle of refraction close to 30°
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Answer: —
At Brewster's angle, tan(i) = μ = 1.73 ≈ √3, so i = 60°. At this angle the reflected ray is completely polarized and the angle of reflection equals the angle of incidence, 60°. (The refracted/transmitted ray is only partially polarized.)

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Q5NEET 2025Polarization - Malus's Law
The intensity of transmitted light when a polaroid sheet, placed between two crossed polaroids at 22.5° from the polarization axis of one of the polaroid, is (I0 is the intensity of polarised light after passing through the first polaroid):
- A. I0/2
- B. I0/4
- C. I0/8
- D. I0/16
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Answer: B — I0/4
After the middle polaroid at 22.5°: I0cos²(22.5°). After the last polaroid at 90° from first (so 67.5° from middle): I0cos²(22.5°)sin²(22.5°) = I0×(1/4)sin²(45°) = I0×(1/4)×(1/2) = I0/8.
Q6NEET 2024Young's Double Slit Experiment with White Light
If the monochromatic source in Young's double slit experiment is replaced by white light, then
- A. there will be a central bright white fringe surrounded by a few coloured fringes.
- B. all bright fringes will be of equal width.
- C. interference pattern will disappear.
- D. there will be a central dark fringe surrounded by a few coloured fringes.
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Answer: —
Since the central fringe for all colors (wavelengths) forms at the same central point (zero path difference for all wavelengths), it appears white due to the mixing of all colors. Fringes away from the center, having different path differences, appear coloured since different wavelengths produce maxima at different positions.
Q7NEET 2024Polarisation at Brewster's Angle
An unpolarised light beam strikes a glass surface at Brewster's angle. Then
- A. both the reflected and refracted light will be completely polarised
- B. the reflected light will be completely polarised but the refracted light will be partially polarised
- C. the reflected light will be partially polarised
- D. the refracted light will be completely polarised.
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Answer: A — both the reflected and refracted light will be completely polarised
At Brewster's angle, the reflected light is completely (linearly) polarised, while the refracted (transmitted) light is only partially polarised.
Q8NEET 2023Young's Double Slit Experiment - Fringe Angular Separation
For Young's double slit experiment, two statements are given below: Statement I: If screen is moved away from the plane of slits, angular separation of the fringes remains constant. Statement II: If the monochromatic source is replaced by another monochromatic source of larger wavelength, the angular separation of fringes decreases. In the light of the above statements, choose the correct answer from the options given below:
- A. Both statement I and statement II are false.
- B. Statement I is true but Statement II is false.
- C. Statement I is false but Statement II is true.
- D. Both Statement I and Statement II are true.
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Answer: A — Both statement I and statement II are false.
Angular separation θ = λ/d, which does not depend on the screen distance D, so Statement I is true. Since θ = λ/d, increasing wavelength λ actually increases θ (not decreases), so Statement II is false.

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Q9NEET 2022Number of Fringes vs Wavelength
In a Young's double slit experiment, a student observes 8 fringes in a certain segment of screen when a monochromatic light of 600 nm wavelength is used. If the wavelength of light is changed to 400 nm, then the number of fringes he would observe in the same region of the screen is:
- A. 6
- B. 8
- C. 9
- D. 12
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Answer: C — 9
Number of fringes in a fixed region is inversely proportional to wavelength (N proportional to 1/lambda) since fringe width is proportional to lambda. N2 = N1 x (lambda1/lambda2) = 8 x (600/400) = 12.
Q10NEET 2020Effect of changing slit separation and screen distance on fringe width
In Young's double slit experiment, if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled, then the fringe width becomes:
- A. double
- B. half
- C. four times
- D. one-fourth
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Answer: B — half
Fringe width β = λD/d. If d is halved and D is doubled, β' = λ(2D)/(d/2) = 4×(λD/d) = 4β, so it becomes four times.

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