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

At a given point on the direction of propagation of electromagnetic wave, if instantaneous values of induced electric and magnetic field are respectively E and B then,
`c=(E )/(B)`
`therefore B=(E )/(c )`
`therefore B=(6.3)/(3xx10^(8))`
`therefore B=2.1xx10^(-8)T` (tesla)
We know that, direction of propagation of electromagnetic waves = direction of `vec(E )xx vec(B)`
`therefore hat(i)=hat(j)xx` (Direction of `vec(B)`)
`rArr` Direction of `vec(B)=` Direction of `hat(k)(because hat(i)=hat(j)xx hat(k))`
= Direction of + Z axis
Final answer :
`vec(B)=B hat(k)`
`therefore vec(B)=2.1xx10^(-8)hat(k)` tesla (T)