The ratio of contributions made by the electric field and magnetic field components to the intensity of an EM wave is

We know that the average energy of an electromagnetic wave is related to the electric field as

Where E₀ and are the amplitude of the electric field and permittivity of vacuum respectively.

And to the magnetic field as,

Where B₀ and are the amplitude of the magnetic field and permeability of vacuum respectively.

Now, we know that E₀ and B₀ are related as

Where c is the speed of the wave, therefore,

But

Therefore, electric and magnetic fields contribute equally, to the electromagnetic wave, thus the ratio of their contributions is 1:1