A ray of light passing through an equilateral prism is having velocity 2.12 × 10⁸ m/s in the prism material, then the minimum angle of deviation is ______ degrees. (a) 45 (b) 30 (c) 28 (d) 58

Answer: (b). μ = c/v = (3×10⁸)/(2.12×10⁸) ≈ 1.414 = √(2) μ = (sin (A+δm)/(2))/(/2) with A = 60°: sin (60°+δm)/(2) = √(2)×1/2 = 1/√(2) (60°+δm)/(2) = 45° ⇒ δm = 30° So the answer is (b) 30°.

A ray of light passing through an equilateral prism is having… | JEE Main 2026 (5 Apr, Shift 1)

Q7JEE Main 2026 · 5 APR · SHIFT 1Medium

Prism, Dispersion & Scattering

A ray of light passing through an equilateral prism is having velocity $2.12 \times 10^{8}\text{ m/s}$ in the prism material, then the minimum angle of deviation is

______ degrees.

Show answer and solution

Answer: (b)

$\mu = \dfrac{c}{v} = \dfrac{3\times10^8}{2.12\times10^8} \approx 1.414 = \sqrt{2}$
$\mu = \dfrac{\sin\frac{A+\delta_m}{2}}{\sin\frac{A}{2}}$ with $A = 60^\circ$ : $\sin\frac{60^\circ+\delta_m}{2} = \sqrt{2}\times\frac{1}{2} = \frac{1}{\sqrt{2}}$
$\frac{60^\circ+\delta_m}{2} = 45^\circ \Rightarrow \delta_m = 30^\circ$
So the answer is (b) $30^\circ$ .

Report a mistake

Prism, Dispersion & Scattering question from JEE Main 2026 (5 Apr, Shift 1)

More questions on Prism, Dispersion & Scattering