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 7.00 km from the source, a detector measures the intensity of the wave to be 35.0 mu W/m^2. What is the peak value of the magnetic field at the detector due to the wave? 1.71E-6 T You have an expression for the intensity of an electromagnetic wave in terms of the electric field or magnetic field. Note that the problem asks for the peak value of B, rather than the rms value. What is the average power radiated by the source? Now the detector is replaced with a perfectly absorbing sheet normal to the incident flux, with surface area 2.30 m^2. What is the force on the sheet due to the wave?

Explanation / Answer

I = c B^2 / 2 u0

35 x 10^-6 = (3 x 10^8) B^2 / (2 x 4 pi x 10^-7)

B = 5.42 x 10^-10 T .........Ans

I= P / (4 pi R^2)

P = 4 pi R^2 I

P = (4 x pi x (7 x 10^3)^2) (35 x 10^-6)

P = 21551.33 W .........Ans

Force = I A / c

= (35 x 10^-6) (2.30) / (3 x 10^8)

= 2.68 x 10^-13 N ..........Ans

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