Communications satellites generally occupy a special orbit in which they go comp

Question

Communications satellites generally occupy a special orbit in which they go completely around the Earth once a day; since the Earth also turns once a day, the satellite is therefore always over the same point on the ground. Your satellite dish can then always be pointed at the same location in the sky. A typical electromagnetic signal from a communications satellite might have an intensity of 0.550 pW/m^2 at the surface of the Earth. Your satellite dish collects the energy of the electromagnetic signal from the satellite; then your dish passes that energy to its central receiver, where the signal can be processed by a circuit. The area of a satellite dish can be calculated from pi (3.1416) times the radius squared. If your satellite dish has a radius of 0.20 m, and if it is receiving the signal described above, how much electromagnetic energy is reflected to the central receiver in 2.5 minutes? Give your answer in picojoules.

Explanation / Answer

given

I = 0.55 PW/m^2 = 0.55*10^-12 W/m^2

r = 0.2 m

t = 2.5 min = 2.5*60 s

we know, Intensity = Power/Area

Power = Intensity*Area

Energy reflected = Power*time taken

= Intensity*Area*time taken

= 0.55*10^-12*pi*0.2^2*2.5*60

= 10.4*10^-12 J

= 10.4 pJ <<<<<<-------------Answer

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