Q131 / 200 · NEET 2021 · Physics

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

Solution

Direction $= \vec{E} \times \vec{B}$

(i) $(\hat{j} + \hat{k}) \times (\hat{j} + \hat{k}) = 0$

(ii) $(- \hat{j} + \hat{k}) \times (- \hat{j} - \hat{k})$

$= 0 + \hat{ı} - (- \hat{ı}) + 0$

$= 2 \hat{ı}$

(iii) $(\hat{j} + \hat{k}) \times (- \hat{j} - \hat{k}) = 0$

(iv) $(- \hat{j} + \hat{k}) \times (- \hat{j} + \hat{k})$

$= 0$

Hence, the correct answer is option: 'B'.