A magnetic field vector in an electromagnetic wave is represented by vec B = B 0sin (2πnu t - 2π x/λ )hat j . Its associated electric field vector is

-nuλ B 0sin (2πnu t - 2π x/λ )hat k

-nuλ B 0sin (2πnu t - 2π x/λ )hat i

nuλ B 0sin (2πnu t - 2π x/λ )hat k

nuλ B 0sin (2πnu t - 2π x/λ )hat i

Physics · Electromagnetic Waves

JEE Main 2026 — 4 April, Evening Shift — Question 14

A magnetic field vector in an electromagnetic wave is represented by $\vec{B} = B_0\sin\left(2\pi\nu t - \frac{2\pi x}{\lambda}\right)\hat{j}$ . Its associated electric field vector is

Option A:
$-\nu\lambda B_0\sin\left(2\pi\nu t - \frac{2\pi x}{\lambda}\right)\hat{k}$
Correct
Option B:
$-\nu\lambda B_0\sin\left(2\pi\nu t - \frac{2\pi x}{\lambda}\right)\hat{i}$
Option C:
$\nu\lambda B_0\sin\left(2\pi\nu t - \frac{2\pi x}{\lambda}\right)\hat{k}$
Option D:
$\nu\lambda B_0\sin\left(2\pi\nu t - \frac{2\pi x}{\lambda}\right)\hat{i}$

Answer: A

Step-by-step solution

For EM wave, $\vec{E}\times\vec{B}$ is along propagation direction $\hat{i}$ . Given $\vec{B} = B_0\sin(\dots)\hat{j}$ , then $\vec{E}$ must be along $\pm\hat{k}$ with $E_0/B_0 = c = \nu\lambda$ . The correct direction gives $\vec{E} = -\nu\lambda B_0\sin(\dots)\hat{k}$ .

Answer key and solution verified before publishing.

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Exam: JEE Main 2026
Paper: 4 April, Evening Shift
Subject: Physics
Chapter: Electromagnetic Waves
Topic: Displacement Current and Equation of EM Waves