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

Explanation

The magnitude of B 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, `E xx B` should be along x - direction. Since, `(+hat(j))xx (+hat(k))=hat(i)`, B is along the z-direction. Thus `B=2.1xx10^(-8)hat(k)T`.