The intensity of the sunlight reaching Earth is 1380 W m−2. Assume this light to be a plane, monochromatic wave. Find the amplitudes of electric and magnetic fields in this wave.
Given: The intensity of sunlight reaching the earth = 1380 W m-2.
We have to find the amplitudes of electric and magnetic field if the
light is a plane electromagnetic wave. The amplitude of the electric
field is related to the intensity of the wave by the relation
where
ϵ0 is the electric permittivity of free space(vacuum) and is equal to 8.85 × 10-12 C2 N-1 m-2
C is the speed of light in vacuum and is equal to 3 × 108 m s-1
and E0 is the amplitude of electric field.
The amplitudes of electric and magnetic fields in free space are related as
where B0 is the amplitude of magnetic field in free space.
Thus the value of magnetic field will be
The electric field amplitude is 
and the magnetic field amplitude is
.