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

Question

A)

A source of electromagnetic waves radiates power uniformly in all directions at a single frequency. At a distance of 3.50 km from the source, a detector measures the intensity of the wave to be 24.0 ?W/m2. What is the peak value of the magnetic field at the detector due to the wave?

B) What is the average power radiated by the source?

C) Now the detector is replaced with a perfectly absorbing sheet normal to the incident flux, with surface area 2.20 m2. What is the force on the sheet due to the wave?

Explanation / Answer

Intensity of wave I = 24 muW/m2

The intensity of em wave is given by I = 1/2 * e0 c Emax2

Emax = c Bmax

I = 1/2 * e0 c (c Bmax)2

24 * 10-6 = 1/2 * 8.85 * 10-12 * (3 * 108)3 * (Bmax)2

Bmax = 4.48 * 10-10 T

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Power P = I (4 pi r2)

= (24 * 10-6) (4 pi * 35002)

P = 3694.5 W = 3.69 * 103 W

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