A source of electromagnetic waves radiates power uniformly in all directions at

Question

A source of electromagnetic waves radiates power uniformly in all directions at a single frequency. At a distance of 6.50 km from the source, a detector measures the intensity of the wave to be 22.0 W/m2. What is the peak value of the magnetic field at the detector due to the wave?
(in T)

What is the average power radiated by the source?
(in W)

Now the detector is replaced with a perfectly absorbing sheet normal to the incident flux, with surface area 1.60 m2. What is the force on the sheet due to the wave?
(in N)

A: 9.00×10-11 B: 1.13×10-10 C: 1.41×10-10 D: 1.76×10-10 E: 2.20×10-10 F: 2.75×10-10 G: 3.43×10-10 H: 4.29×10-10

Explanation / Answer

Here ,

intensity of wave , I = 22 uW/m^2

distance , d = 6.5 km

d = 6500 m

a)

let the amplitude of magnetic field is Bm

I = c*Bm^2/(2*u0)

22 *10^-6 = 3 *10^8 * Bm^2/(2 * 4pi *10^-7)

Bm = 4.29 *10^-10 T

the amplitude of magnetic field is H. 4.29 *10^-10 T

part B)

let the power is P

intensity = P/(4 *pi * d^2)

22 *10^-6 = P/(4 * pi * 6500^2)

P = 1.17 *10^4 W

the average power radiated by the source is C. 1.17 *10^4 W

part c)

for the perfect absorber

Force on the sheet = pressure * area

Force on the sheet = (22 *10^-6) * 1.6/(3 *10^8)

Force on the sheet = 1.17 *10^-13 N

the force on the sheet due to wave is A. 1.17 *10^-13 N

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