Physics · Wave Optics

JEE Main 2025 — 2 April, Morning Shift — Question 55

A light wave is propagating with plane wave fronts of the type $x+y+z=$ constant. The angle made

by the direction of wave propagation with the $x$ -axis is

Option A:
$\cos ^{-1}\left(\frac{2}{3}\right)$
Option B:
$\cos ^{-1}\left(\frac{1}{\sqrt{3}}\right)$
Correct
Option C:
$\cos ^{-1}\left(\frac{1}{3}\right)$
Option D:
$\cos ^{-1}\left(\sqrt{\frac{2}{3}}\right)$

Answer: B

Step-by-step solution

Direction of propagation $\vec{A}=\hat{i}+\hat{j}+\hat{k}$

\begin{aligned} \text { Angle with } x \text {-axis } & =\cos ^{-1}\left(\frac{A x}{\sqrt{A_{x}^{2}+A_{y}^{2}+A_{z}^{2}}}\right) & =\cos ^{-1}\left(\frac{1}{\sqrt{3}}\right) \end{aligned}

Answer key and solution verified before publishing.

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Exam: JEE Main 2025
Paper: 2 April, Morning Shift
Subject: Physics
Chapter: Wave Optics
Topic: Huygens' Wave Theory and Wavefronts

If the measured angular separation between the second minimum to the left to the central maximum and the third minimum to the right of the…