PYQ NEET- Electromagnetic Waves L-8

Question: An EM wave is propagating in a medium with a velocity $\vec{v}=v \hat{i}$. The instantaneous oscillating electric field of this em wave is along $+y$ axis. Then the direction of oscillating magnetic field of the em wave will be along (NEET-2018)#

A) $z$ direction

B) $+z$ direction

C) $-y$ direction

D) $-x$ direction

Answer: $+z$ direction#

Explanation#

As we know,

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

$\Rightarrow E \hat{j} \times \vec{B}=v \hat{i}$

[ As given Electric field vector is along $+y$ axis and $\vec{v}=v \hat{i}$ ]

$\hat{i}=\hat{j} \times \widehat{k} \text { so } \vec{B}=B \widehat{k}$

$\therefore$ Direction of magnetic field vector is along $+\mathrm{z}$ direction.