A plane electromagnetic wave travels in vacuum along z - direction. What can you say about the directions of its electric and magnetic field vectors ? If the frequency of the wave is 30 MHz, what is its wavelength ?

Explanation

Here `vec(E )` must be along + X axis and `vec(B)` must be along + Y axis, so that direction of `vec(E )xx vec(B)=` direction of `hat(i)xx hat(j)=` direction of `hat(k)=` direction of + Z axis = direction of propagation of electromagnetic wave.
In both of above cases, `vec(E )` and `vec(B)` will oscillate perpendicular to each other in XY - plane, perpendicular to direction of propagation of electromagnetic wave.
Since given electromagnetic wave propagates in vacuum, its speed would be equal to c. Now, according to formula,
`c=v lambda`
`therefore lambda = (c )/(v)=(3xx10^(8))/(30xx10^(6))=10m`