An electromagnetic wave is transporting energy in the negative $z$ direction. At a certain point and certain time the direction of electric field of the wave is along positive $y$ direction. What will be the direction of the magnetic field of the wave at that point and instant?
Solution
As, poynting vector<br/><br/>
$$
\overrightarrow{\mathrm{S}}=\overrightarrow{\mathrm{E}} \times \overrightarrow{\mathrm{H}}
$$<br/><br/>
Given energy transport $=$ negative $\mathrm{z}$ direction<br/><br/> Electric field $=$ positive $\mathrm{y}$ direction <br/><br/>$(-\hat{\mathrm{k}})=(+\hat{\mathrm{j}}) \times[\hat{\mathrm{i}}]$<br/><br/>
Hence according to vector cross product magnetic field should be positive $\mathrm{x}$ direction.
About this question
Subject: Physics · Chapter: Electromagnetic Waves · Topic: Properties of EM Waves
This question is part of PrepWiser's free JEE Main question bank. 109 more solved questions on Electromagnetic Waves are available — start with the harder ones if your accuracy is >70%.