# Power in beam of light given amplitude

by Cspeed
Tags: amplitude, beam, light, power
 P: 44 I would like to calculate the power of a beam of light once I know the electric field amplitude. For example if I know the amplitude along a line from -1 meter to +1 meter every 0.5 m is [1, 2, 2.5, 2, 1 V/m], how can I find the power from this is? Is there enough info? (it's in vacuum/air) Thank you.
 Mentor P: 9,634 Energy density is proportional to the squared amplitude (see Wikipedia for example), and power is just average energy density times the speed of light. Don't forget the magnetic component, which is 50% of the total power.
 P: 44 Thanks, but I'm not sure still. I knew that power was proportional to the square of amplitude, but I'm hoping to get a figure in watts. I see that I need H as well. But how does this all fit in to my 1-D scenario?
Mentor
P: 9,634

## Power in beam of light given amplitude

You get W/m^2 - what else did you expect? If the source emits radiation uniform in space, you can multiply that with the corresponding sphere surface area to get the total power.

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