1. j+k,\ j+k 2. -j+k,\ -j-k 3. j+k,\ -j-k 4. -j+k,\ -j+k

Answer: 2. -j+k,\ -j-k Key idea: vec E , vec B and the direction of propagation are mutually perpendicular, and vec E×vec B points along propagation (+x). Option 1: E and B parallel, so cross product is zero. Wrong. Option 2: (-hat j+hat k)×(-hat j-hat k)=hat i+hat i=2hat i , along +x, and E· B=1-1=0 . Correct. Option 3: E and B antiparallel, cross product zero. Wrong. Option 4: E and B parallel. Wrong.

Topic: EM waves, characteristics and transverse nature· Electromagnetic Waves

For a plane electromagnetic wave propagating in x-direction, which one of the following combination gives the correct possible directions for electric field (E) and magnetic field (B) respectively ?

1. \(\hat{j}+\hat{k},\ \hat{j}+\hat{k}\)

2. \(-\hat{j}+\hat{k},\ -\hat{j}-\hat{k}\)

3. \(\hat{j}+\hat{k},\ -\hat{j}-\hat{k}\)

4. \(-\hat{j}+\hat{k},\ -\hat{j}+\hat{k}\)

Doubtly Asked 30 Oct 2026 NEET UG 2021 Practice test neet Save WhatsApp Report

1 answer

Best answer

Answer: 2. \(-\hat{j}+\hat{k},\ -\hat{j}-\hat{k}\)

Key idea: \(\vec E\), \(\vec B\) and the direction of propagation are mutually perpendicular, and \(\vec E\times\vec B\) points along propagation (+x).

Option 1: E and B parallel, so cross product is zero. Wrong.
Option 2: \((-\hat j+\hat k)\times(-\hat j-\hat k)=\hat i+\hat i=2\hat i\), along +x, and \(E\cdot B=1-1=0\). Correct.
Option 3: E and B antiparallel, cross product zero. Wrong.
Option 4: E and B parallel. Wrong.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

Was this answer helpful?

For a plane electromagnetic wave propagating in x-direction, which one of the following combination gives the correct possible directions for electric field (E) and magnetic field (B) respectively ?

1 answer

Your answer