A small helium-neon laser emits red visible light with a power of 3.85 mW in a b

Question

A small helium-neon laser emits red visible light with a power of 3.85 mW in a beam that has a diameter of 2.80 mm.

A small helium-neon laser emits red visible light with a power of 3.85 mW in a beam that has a diameter of 2.80 mm. What are the amplitudes of the electric and magnetic fields of the light? Emax = V/m Bmax = T What are the average energy densities associated with the electric field and with the magnetic field? UE, av = J/m3 UB, av = J/m3 What is the total energy contained in a 1.00-m length of the beam? J

Explanation / Answer

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INTENSITY = POWER/AREA = E^2/?0C

E^2 = 3.7 *10^-3*4*3.14*10^-7*3*10^8/4*3.14 *1.7*1.7*10^10^-6

E^2 = 3840

E = 61.96 V/m

B = E/c = 20.6 *10^-8 T

B) UB = B^2/2?0 = 20.6*20.6/2*4*3.14*10^-7 = 16.98 *10^7

Ue = 0.5 ?0 E^2 = 0.5*8.85*10^-12*61.96*61.96 = 16987*10^-12   

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