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.
The word "intensity" as used here is not synonymous with "strength", "amplitude", "magnitude", or "level", as it sometimes is in colloquial speech.
The intensity of a wave is proportional to the square of its amplitude.
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.
Applying the law of conservation of energy, if the net power emanating is constant,
where If one integrates a uniform intensity, |I| = const., over a surface that is perpendicular to the intensity vector, for instance over a sphere centered around the point source, the equation becomes
If the medium is damped, then the intensity drops off more quickly than the above equation suggests.
and the local intensity is obtained by multiplying this expression by the wave velocity,
where For non-monochromatic waves, the intensity contributions of different spectral components can simply be added.
The treatment above does not hold for arbitrary electromagnetic fields.
For example, an evanescent wave may have a finite electrical amplitude while not transferring any power.
The intensity should then be defined as the magnitude of the Poynting vector.
[1] For electron beams, intensity is the probability of electrons reaching some particular position on a detector (e.g. a charge-coupled device[2]) which is used to produce images that are interpreted in terms of both microstructure of inorganic or biological materials, as well as atomic scale structure.
[3] The map of the intensity of scattered electrons or x-rays as a function of direction is also extensively used in crystallography.
[3][4] In photometry and radiometry intensity has a different meaning: it is the luminous or radiant power per unit solid angle.
Radiance is also sometimes called intensity, especially by astronomers and astrophysicists, and in heat transfer.