A microphone of cross-sectional area 0.80 cm2 is placed in front of a small speaker emitting 3.0 W of sound output. If the distance between the microphone and the speaker is 2.0 m, how much energy falls on the microphone in 5.0 s?
powerArea for a sphere of radius 2m is 34π(2)2
Now to get power being received by microphone
316π × 0.80 × 10−4
Energy received in 5 sec
Energy = power × time
316π × 0.80 × 10−4 × 5
=0.238 × 10−4
=24 × 10−6J
=24 μ J