An isotropic point source emits light at wavelength 500 nm, at the rate of 185 W. A light detector is positioned 380 m from the source. What is the maximum rate ∂B/∂t at which the magnetic component of the light changes with time at the detector's location?

Explanation:

Given that

An isotropic point source emits light at a wavelength = 500 nm

Power = 185 W

Radius = 380 m

Let's first calculate the The intensity  of the wave , which is =

=

=  

=

Now;

The amplitude of the magnetic field is calculated afterwards by using poynting vector

i.e

The magnetic field wave equation can now be expressed as;

Taking the differentiation

The maximum value ;

where ;

then