Question

Suppose that a public-address system emits a 494 Hz sound uniformly in all directions. (a) If the air temperature is 25oC (sound travels at 346 m/s), what is the wavelength of this sound? (b) If the intensity at a location 22 m away from the sound source is 3x10-4 W/m2 , what is the power of the sound coming from the speaker?

Answer 1

a)
$v = f\lambda$

$\lambda = \frac{v}{f}$

$\lambda = \frac{346}{494}$

$\lambda = 0.7 m$

b)

Assuming that spherical wave is emitted from the source,

$P = I * 4\pi R^{2}$

$P =(3*10^{-4}) * 4\pi *22^{2}$

$P =1.8246 W$