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SOLUTIONS TO EXERCISE 9
(a) F = L/(4 pi r^2); L 0.002 W/m^2 = --------------------- ; so 4 * 3.14 * (10^6 m)^2 0.002 W/m^2 * 4 * 3.14 * (10^6 m)^2 = L = 2.5 * 10^10 W. (b) F = L/(4 pi r^2); 2000 W 2000 W 0.015 W/m^2 = -------------- ; so r^2 = ---------------------- 4 * 3.14 * r^2 4 * 3.14 * 0.015 W/m^2 r = sqrt(10615 m^2) = 103 m. |