This is an example of the inverse-square law.Īpplying the law of conservation of energy, if the net power emanating is constant, If a point source is radiating energy in all directions (producing a spherical wave), and no energy is absorbed or scattered by the medium, then the intensity decreases in proportion to the distance from the object squared. For example, the intensity of an electromagnetic wave is proportional to the square of the wave's electric field amplitude. The intensity of a wave is proportional to the square of its amplitude. The resulting vector has the units of power divided by area (i.e., surface power density). Intensity can be found by taking the energy density (energy per unit volume) at a point in space and multiplying it by the velocity at which the energy is moving. The word 'intensity' as used here is not synonymous with ' strength', ' amplitude', ' magnitude', or ' level', as it sometimes is in colloquial speech. For example, one could calculate the intensity of the kinetic energy carried by drops of water from a garden sprinkler.

Intensity can be applied to other circumstances where energy is transferred. Intensity is used most frequently with waves such as acoustic waves ( sound) or electromagnetic waves such as light or radio waves, in which case the average power transfer over one period of the wave is used. In the SI system, it has units watts per square metre (W/m 2), or kg⋅ s −3 in base units.

In physics, the intensity or flux of radiant energy is the power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy. For other uses, see Intensity (disambiguation).

Light intensity from sin equation