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# A plane electro magnetic wave of frequency $25\;MHz$ travels in free space along the x- direction At a particular point in space and time the electric vector $\overrightarrow{E}= 6.3 v/m \hat j$. calculate $\overrightarrow{B}$ at this point .

$\begin{array}{1 1} 2.1 \times 10^{-7} \hat k \;t \\ 2.1 \times 10^{-8} \hat k \;t \\ 2.1 \times 10^{-8} \hat j \;t \\ 2.1 \times 10^{-7} \hat j \;t \end{array}$

$B= \large\frac{E}{C}$
$\quad= \large\frac{6.3 v/m}{3 \times 10^8m/s}$
$\quad= 2.1 \times 10^{-8}\;T$
As $\overrightarrow{E}$ is along y- direction and wave is travelling along x- direction .
$\overrightarrow{B}$ is along z direction
$\qquad= 2.1 \times 10^{-8} \hat k \;t$