Calculate the sound intensity 6 m from a loudspeaker of power 20 mW. - Leaving Cert Physics - Question g - 2021

Since sound propagates uniformly in all directions, the area (A) can be calculated as the surface area of a sphere:

$A = 4 \pi r^2$

For this problem, the distance (r) is 6 m:

$A = 4 \pi (6)^2 = 144 \pi \, \text{m}^2 \approx 452.39 \, \text{m}^2$

Now substituting the values into the intensity formula:

• The power (P) of the loudspeaker is 20 mW, which is equal to 0.02 W.

$I = \frac{0.02}{452.39} \approx 4.42 \times 10^{-5} \text{W m}^{-2}$