Question

The electric and the magnetic field, associated with an $EM$ wave, propagating along the $+z$-axis, can be represented by

• A. $\overrightarrow{E}=E_0\hat{j},\overrightarrow{B}=B_0\hat{k}$
• B. $\overrightarrow{E}=E_0\hat{i},\overrightarrow{B}=B_0\hat{j}$
• C. $\overrightarrow{E}=E_0\hat{k},\overrightarrow{B}=B_{\circ }\hat{i}$
• D. $\overrightarrow{E}=E_0\hat{j},\overrightarrow{B}=B_0\hat{i}$

Answer 1

The correct option is B $\overrightarrow{E}=E_0\hat{i},\overrightarrow{B}=B_0\hat{j}$

If wave is propagating in $+z$ direction then $\overrightarrow{E}$ and $\overrightarrow{B}$ will be in $x-y$ plane.

Also, $\overrightarrow{E}\times \overrightarrow{B}=$ direction of propagation of wave ($+z$ direction).

In option $\left(a\right)$ magnetic field is given along $+z$-axis which is not possible.

In option $\left(c\right)$ electric field is given along $+z$-axis which is also not possible.

In option $\left(d\right)$ electric and magnetic field is given along $+y$-axis and $+x$-axis respectively. But based on their directions the direction of propagation of the wave is along $-z$-axis which is opposite to that given in question.

Since, option $\left(b\right)$ satisfies all the conditions.

Hence, option$\left(B\right)$ is the correct answer.