Source of EM wave Points:3 A source of electromagnetic waves radiates power unif

Question

Source of EM wave Points:3 A source of electromagnetic waves radiates power uniformly in all directions at a single frequency. At a distance of 4.50 km from the source, a detector measures the intensity of the wave to be 30.0 W/m2, what is the peak value of the magnetic field at the detector due to the wave? 5.01E-7T-0 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. Submit Answer Unable to interpret units. Computer reads units as "T-o". Tries 2/12 Previous Tries What is the average power radiated by the source? Submit Answer Tries 0/12 Now the detector is replaced with a perfectly absorbing sheet normal to the incident flux, with surface area 1.90 m2. What is the Submit Answer Tries 0/12 force on the sheet due to the wave?

Explanation / Answer

Given,

R = 4.5 km ; I = 30 uW/m^2

We know that,

I = B^2 c/2 u0

B = sqrt (2 u0 I/c)

B = sqrt (2 x 4 x 3.14 x 10^-7 x 30 x 10^-6/(3 x 10^8)) = 5.012 x 10^-10 T

Hence, B = 5.012 x 10^-10 T

The average power will be given by:

P = IA = I (4 pi R^2)

P = 30 x 10^-6 x 4 x 3.14 x (4.5 x 10^3)^2 = 7630.2 W

Hence, P = 7630.2 W

We know that,

Radiation Pressure = I/c = 30 x 10^-6/(3 x 10^8) = 1 x 10^-13 Pa

P = F/A => F = PA

F = 1 x 10^-13 x 1.9 = 1.9 x 10^-13 N

Hence, F = 1.9 x 10^-13 N

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