A plane electromagentic wave of frequency 25 MHz travels in free space along the x-direction. At a particular point in space and time , E=6.3 `hatj` V/m . What is B at the point ?

Explanation

The magnitude of `hatB` is
`B=(E)/(C)=(6.3V//m)/(3xx10^(8)m//s)=2.1xx10^(-8)T`
To find the direction, we note that E is along y-direction and the wave propagates along x-axis. Therefore, B should be in a direction perpendicular to both x-and y-axes. Using vector algebra, `ExxB` should be along x-direction. Since, `(+hatj)xx(+hatk)=hatiB` is along the z-direction.
Thus, `barB=2.1xx10^(-8)hatkT`.