e) Intensity

g) intensity of a progressive wave; I = P/A; intensity ∝ (amplitude)²

intensity = power transferred by a wave onto a surface per its unit area

I = P/A

• intensity of a wave (Wm^-2) = power transferred by the wave (W) / area of the surface (m²)

if the wave originates from a point source

I = P/4πr²

• intensity of a wave (Wm^-2) = power transferred by the wave (W) / (4 × π × distance from the surface to the source² (m²) )

intensity ∝ amplitude²