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NEET Ray Optics and Wave Optics: 5 practice MCQs

By the PrepMatic team · Updated 9 Oct 2026 · 3 min read

Optics is a favourite NEET Physics unit because it mixes sign-convention numericals with clean theory. The five MCQs below cover the image in a concave mirror, the critical angle, lens power, the refractive index of a prism and fringe width in Young's double slit experiment, at NCERT Class 12 level.

What this chapter covers in the NEET syllabus

The NMC lists a single unit called Optics. In NCERT it spans the Class 12 chapters Ray Optics and Optical Instruments, and Wave Optics. The topics are:

• Reflection from plane and spherical mirrors, the mirror formula and magnification.
• Refraction, Snell's law, total internal reflection and its uses.
• Refraction at spherical surfaces, thin lenses, the lens maker's formula and lens power.
• Refraction and dispersion by a prism.
• Optical instruments: the human eye, microscope and astronomical telescope.
• Wave optics: Huygens' principle, interference, Young's double slit experiment, diffraction and polarisation.

Five practice MCQs on Optics

Question 1

An object is placed 30 cm in front of a concave mirror of focal length 15 cm. The image is formed:

• A. 15 cm behind the mirror
• B. 30 cm in front of the mirror
• C. 10 cm in front of the mirror
• D. at infinity

Question 2

The critical angle for light going from a medium of refractive index √2 into air is:

• A. 30°
• B. 60°
• C. 45°
• D. 90°

Question 3

A convex lens has a focal length of 25 cm. Its power is:

• A. +25 D
• B. +0.25 D
• C. +2.5 D
• D. +4 D

Question 4

An equilateral prism of angle 60° has a minimum deviation of 30°. The refractive index of its material is:

• A. √2
• B. 1.5
• C. 1.33
• D. √3

Question 5

In Young's double slit experiment, the slit separation is 1 mm, the screen is 1 m away and the wavelength is 600 nm. The fringe width is:

• A. 6 mm
• B. 1.2 mm
• C. 0.6 mm
• D. 0.3 mm

Answers and explanations

1. B. Using 1/v + 1/u = 1/f with u = −30 and f = −15: 1/v = −1/15 + 1/30 = −1/30, so v = −30 cm. The object is at the centre of curvature (2f), so the image is real, inverted, the same size, and formed at the same point, 30 cm in front.
2. C. sin C = 1/n = 1/√2, so C = 45°. Total internal reflection occurs only when light travels from a denser to a rarer medium at an angle of incidence greater than C.
3. D. Power is P = 1/f with f in metres, so P = 1/0.25 = +4 D. The positive sign is for a converging lens. Option B comes from using centimetres in the formula.
4. A. n = sin[(A + δm)/2]/sin(A/2) = sin 45°/sin 30° = 0.7071/0.5 = √2 ≈ 1.41. At minimum deviation the ray passes symmetrically through the prism.
5. C. Fringe width β = λD/d = (600 × 10⁻⁹ × 1)/(1 × 10⁻³) = 6 × 10⁻⁴ m = 0.6 mm. Keep all lengths in metres before dividing.

How to prepare Optics

• Choose one sign convention and keep it. Use the Cartesian convention: distances measured from the pole along the incident light are positive. Then the mirror formula 1/v + 1/u = 1/f and the lens formula 1/v − 1/u = 1/f apply directly, with no sign changes between questions.
• Draw the ray diagram first. Before substituting numbers, sketch where the object lies relative to f and 2f, so you know whether to expect a real or virtual image. It catches sign errors immediately.
• Memorise a small set of results. Lens maker's formula, combination of thin lenses (P = P1 + P2 for lenses in contact), prism formula, critical angle sin C = 1/n, and the condition for total internal reflection.
• Treat wave optics as formulas plus ideas. Know the path difference conditions for bright and dark fringes (nλ and (n + ½)λ), how fringe width changes with λ, D and d, and the difference between interference and diffraction patterns.
• Learn the instruments. Magnifying power of a simple microscope, compound microscope and telescope in normal adjustment.

Work through the ray-optics numericals first, then wave optics, since the latter is shorter. For the subject-level plan, see the NEET Physics preparation guide, and check the NEET syllabus for the unit list.

Take a full Ray and Wave Optics test on PrepMatic

A timed test is the best check on your sign-convention habits in Optics. PrepMatic's topic tests run about 15 questions in 30 minutes and apply NEET's negative marking. They are part of the free Basic plan, and more chapters are on the practice hub.

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