In
physics,
intensity is the
power transferred per unit
area, where the area is an imagined surface that is perpendicular to the direction of propagation of the energy. In the
SI system, it has units watts per square metre (W/m
2). It is used most frequently with
waves (e.g.
sound or
light), in which case the
average power transfer over one
period of the wave is used.
Intensity can be applied to other circumstances where energy is transferred. For example, one could calculate the intensity of the
kinetic energy carried by drops of water from a
garden sprinkler.