rms (physics) help?

Question

I'm trying to find the rms values of E (electric field) and B (manetic field). I'm only given power and the diameter of the laser beam. I'm not sure where to start with the problem.

Answer 1

Generally, it's most useful to use the average power, or average intensity, of the wave. To find the average values, you have to use some average for the electric field E and the magnetic field B. The root mean square averages are used; the relationship between the peak and rms values is:

Erms = E0/(2)^(1/2)
Brms = B0/(2)^(1/2)

Answer 2

Teo's answer is correct, but only if your two fields follow a sinusoidial wave, e.g., E sin(theta(pi ft) + phase); where theta is the waveform angle as a function of time and frequency, and phase is some angular (in pi units) offset relative to time t = 0.

RMS has different results for other wave shapes...like a square wave for example. [See source.]