1. A source of sound radiates 10.0 watts.

 What power is incident on one square metre of a sphere of radius 1 m?

Answer:
Area of sphere = 4p r2 = 4p(1)2 = 12.6 m2
P/A = 10W/12.6 m2 = 0.796 W/m2
Therefore the power on 1 m2 is 0.796 W.

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