A circular uniform laser beam has a power of P = 4.9 mW and a diameter of d = 4.

Question

A circular uniform laser beam has a power of P = 4.9 mW and a diameter of d = 4.5 mm. The beam is a form of electromagnetic radiation with both electric (E0) and magnetic (B0) field components.

c)Use the intensity of the beam (I) to calculate the amplitude of the electric field E0 in units of V / m.

(d)The amplitudes of the electric and magnetic fields in an electromagnetic wave have a fixed relationship. Based on that relationship, use the result in Part (c) to calculate the amplitude of the magnetic field (B0) in units of Tesla.

Explanation / Answer

P = 4.9 mW, d = 4.5 mm, A = pi*d^2

intensity I = P/A

I = 4.9*0.001/(3.14*(4.5*0.001)^2)

I = 77.1 W/m^2

Intensity I = 0.5*eo*Eo^2*c

77.1 = 0.5*8.85*10^-12*Eo^2*3*10^8

Eo = 241 N/C

Eo/Bo =C

241 = Bo*3*10^8

Bo = 8.03*10^-7 T

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