An industrial laser is used to burn a hole through a piece of metal. The average intensity of the light is = 3.74 × 109 W/m2. What is the rms value of (a) the electric field and (b) the magnetic field in the electromagnetic wave emitted by the laser?
We know that
Intensity and the Poynting Vector are related by the
relation
I = 1/2 |S| = 1/2 ?cE²
Which equals the rms value of epsilon-naught times the speed of
light times the square of the peak value of the electric
field.
Solving for E, we get
|S| = ?cE²
or
|S| / (?c) = E²
E = ?[ |S| / (?c) ]
substituting the values, we get
Erms = ?(3.74 x 109)/(8.854 x 10-12)(3 x 108) = ?(0.141 x 1013) = ?(1.41 x 1012) = 1.19 x 106 V/m
the magnetic field is related to the electric field as
B = E / c
hence
Brms = Erms/c = (1.19 x 106)/( 3 x 108) = 0.4 x 10-2 T
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