# The Intensity At A Point At A Distance R From A Source Which Produces Cylindrical Wavefront Varies As

Dear Student,

A point source produces a spherical wave assuming medium is isotropic(air). Wave energy is conserved as it propagates through air. In a spherical pressure wave of radius r, the energy of wavefront is spread out over the spherical surface area i.e. 4πr squared. Therefore, the energy per unit area of an expanding spherical wave decreases as 1/r squared (Spherical Spreading Loss). Since energy is proportional to amplitude squared, an Inverse Square Law for energy translates to 1/r decay law for amplitude.

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