OnRamps Physics Practice Test

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What is the expression for the sound intensity I in terms of the source power P and the area A over which the power spreads?

I = P*A I = A/P I = P/A I = P^2/A^2

Correct Answer:

I = P/A

Explanation:

Sound intensity is the power per unit area—the rate at which energy passes through a given area. If a source emits power P and that power spreads over an area A, the intensity is I = P/A. This makes intuitive sense: more area means the same amount of power is spread thinner, so the intensity goes down in proportion to 1/A. In free space, a point source radiates over a spherical area A = 4πr^2, giving I = P/(4πr^2). The units are watts per square meter. Expressions that multiply by area or square the power don’t match the idea of energy crossing area, which is why they aren’t correct.

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