You want a screen to be illuminated with a peak intensity of

You want a screen to be illuminated with a peak intensity of 604 mW/m2. If the average power of the source is 800 W, what distance between the screen and the light source is required? What is the rms value of the magnetic field at the screen?

Solution

peak intensity , Io = 604x10^-3 W/m^2

the distance r is calculated as follows:

I = P_av/(4 *pi * r^2)

604x10^-3 = 800 /4 * pi * r^2

solving for r, we get r = 10.26 m

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Intensity, I = c*B_max^2 /2u0

0.604 = B_max^2 *3 *10^8 * /2*(4pi *10^-7)

Bmax = 1.000x10^-7 T

Rms value of field is,

   Brms = Bmax/sqrt[2] = 71.1x10^-9 T