Question

The "ears" of a frog are two circular membranes located behind the frog's eyes. In one species of frog each membrane is 0.500 cm in radius. If a source of sound has a power output of 2.50×10−6W, emits sound equally in all directions, and is located 1.50 m from the frog, how much sound energy arrives at one of the membranes each second?

Answer 1

Power output of the source of sound = P = 2.5 x 10^-6 W

Distance of the frog from the source of the sound = R = 1.5 m

Sound intensity at the location of the frog = I

The sound is equally distributed in all directions.

P = (4R²)I

2.5x10^-6 = 4(1.5)²I

I = 8.842 x 10^-8 W/m²

Radius of each membrane of the frog = r = 0.5 cm = 0.005 m

Sound energy arriving at one of the membranes each second = E

E = (r²)I

E = (0.005)²(8.842x10^-8)

E = 6.944 x 10^-12 W

Sound energy arriving at one of the membranes each second = 6.944 x 10^-12 W