Energy Flux
![](http://scienceworld.wolfram.com/images/gradient-teal.gif)
![](http://scienceworld.wolfram.com/images/spacer.gif)
![](http://scienceworld.wolfram.com/physics/eimg331.gif)
(1)
The mean energy
flux is
![](http://scienceworld.wolfram.com/physics/eimg332.gif)
, also written as
![](http://scienceworld.wolfram.com/physics/eimg333.gif)
and called
I, the
intensity. For a traveling wave,
![](http://scienceworld.wolfram.com/physics/eimg335.gif)
(2)
The unit of energy flux is 1 J m
-2 s
-1 = 1 kg s
-3. For radiation, consider a half-plane filled with
energy density u, then
![](http://scienceworld.wolfram.com/physics/eimg336.gif)
(3)
where
c is the
speed of light,
![](http://scienceworld.wolfram.com/physics/eimg124.gif)
is the angle from the propagation axis,
a is the
radiation constant,
T is the
temperature, and
![](http://scienceworld.wolfram.com/physics/eimg30.gif)
is the
Stefan-Boltzmann constant
Foot Pound
A unit of energy equal to