Question

A plane e.m. wave of frequency 40$MHz$ travels along $X$ -axis, At same point at same instant, the electric field E has maximum value of 750$N/C$ in $Y$ - direction. The magnitude and direction of magnetic field is

• A. 2.5$\mu T$ along $X$ -axis
• B. 2.5$\mu T$ along $Y$ -axis
• C. 2.5$\mu T$ along $Z$ -axis
• D. 5$\mu T$ along $Z$ -axis

Answer 1

The correct option is A 2.5$\mu T$ along $X$ -axis

$EM$ wave travels with velocity of light.

And at every instant $\frac{E}{B}.C$

then,

$\begin{array}{c}\frac{750}{B}=3\times {10}^8\\ B=\frac{750}{3\times {10}^8}=250\times {10}^{-8}\\ =2.5\mu Jalongz-axis.\end{array}$