Everything about Intensity Physics totally explained
In
physics,
intensity is a
measure of the
time-averaged energy flux. The word "intensity" here isn't synonymous with "", "", or "", as it sometimes is in colloquial speech. For example, "the intensity of pressure" is meaningless, since the parameters of those variables don't match.
To find the intensity, take the energy density (that is, the energy per unit volume) and multiply it by the
velocity at which the energy is moving. The resulting
vector has the units of
power divided by
area (for example watt/m²). It is possible to define the intensity of the water coming from a garden sprinkler, but intensity is used most frequently with
waves (for example
sound or
light).
Mathematical description
If a point source is radiating energy in three dimensions and there's no energy lost to the medium, then the intensity decreases in proportion to distance from the object squared. This is due to physics and geometry. Physically,
conservation of energy applies. The consequence of this is that the net power coming from the source must be constant, thus:
»
where
P is the net power radiated,
I is the intensity as a function of position, and
dA is a differential element of a closed surface that contains the source. That
P is a constant. If we integrate over a surface of uniform intensity
I, for instance, over a sphere centered around a point source radiating equally in all directions, the equation becomes:
» ,
where
n is the
refractive index,
is the
speed of light in
vacuum and
is the
electric permittivity in vacuum.
Intensity in photometry and radiometry
In
photometry and
radiometry,
intensity has a different meaning: it's the luminous or radiant power
per unit solid angle. This can cause confusion in
optics, where
intensity can mean any of
radiant intensity,
luminous intensity or
irradiance, depending on the background of the person using the term.
Radiance is also sometimes called
intensity, especially by astronomers and astrophysicists.
Further Information
Get more info on 'Intensity Physics'.
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