11 The light from a 500 mw laser is spread out in a cylinder

11. The light from a 5.00 mw laser is spread out in a cylinder beam whose diameter is about 0.500 cm. What are the peak values of E and B in this beam?

Solution

Area

A=pi*D²/4 =pi*(0.5*10^-2)²/4 =1.963*10^-5 m²

Since Average power

P=(1/2)ce_oAE_m²

=>E_m = sqrt[2P/ce_oA] =sqrt[2*5*10^-3/3*10⁸*8.85*10^-12*1.963*10^-5]

E_m=438 V/m

Peak Value of magnetic field

B_m=E_m/c =438/(3*10⁸)

B_m=1.46*10^-6 T or 1.46 uT