A source of electromagnetic waves radiates power uniformly in all directions at
ID: 1296273 • Letter: A
Question
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 33.0 ?W/m2.
A). 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 2.50 m2. What is the force on the sheet due to the wave?
Explanation / Answer
1) magnetic field = sqrt(2*mue0*intensity/c)
B = sqrt(2*4pi*10^-7*32*10^-6/3*10^8) = 0.0509 T
2) average power = 4pisd^2 = 4*3.14*32*10^-6*(3.5*10^3)^2 = 4923.5 W
3) power = force/area
force = power*area = 8369.98 N
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