## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

We can find the intensity of the sound wave at a distance of 20 m. $I = I_0~10^{\beta/10}$ $I = (10^{-12}~W/m^2)~10^{90/10}$ $I = 10^{-3}~W/m^2$ We can find the power output of the speaker. $P = I~A$ $P = I~(4\pi~R^2)$ $P = (10^{-3}~W/m^2)(4\pi)(20~m)^2$ $P = 5.0~W$ The speaker's power output is 5.0 W.