42.What is the average value of the magnitude of the Poynting vector at 1 meter from a 100-watt lightbulb radiating uniformly in all directions?
(A) 1 W/m2
(B) 2 W/m2
(C) 4 W/m2
(D) 8 W/m2
(E) 16 W/m2
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統計: A(0), B(1), C(0), D(3), E(0) #3427042
統計: A(0), B(1), C(0), D(3), E(0) #3427042