What is the frequency of an electromagnetic wave with energy of 5.0x10-20j?

The frequency of an electromagnetic wave can be calculated using the formula E = hf, where E is the energy, h is Planck's constant (6.626 x 10^-34 J s), and f is the frequency. Rearranging the formula to solve for frequency gives f = E/h. Plugging in the given values, we get f = (5.0 x 10^-20 J) / (6.626 x 10^-34 J s) ≈ 7.54 x 10^13 Hz.