Question

How much energy in kJ is associated with a radio wave of wavelength 1.2 X 10^2 m?

Answer 1

It's very simple.

Energy = $\frac{hc}{\lambda}$

where, h= Planck's constant = 6.6 x $10^{-34}$ $m^2 kg/s$

c= speed of light = 3 x $10^{8}$ m/s
$\lambda$ = wavelength


So, energy = $\frac{6.6 \times 10^{-34} \times 3 \times 10^{8}}{120}$

= 1.65 x $10^{-27}$ J
=1.65 x $10^{-30}$ KJ