PHYSICS - OPTICS This is a variation of a question I asked (same scenario, diffe

Question

PHYSICS - OPTICS

This is a variation of a question I asked (same scenario, different question to solve for).

QUESTION: A 5 mW HeNe laser emits photons of single wavelength 632.8 nm in a beam of light in a vacuum. The beam diameter diverges slightly at a distance 3 m from the laser output. The diameter of the beam is 2 mm. If we use the electromagnetic wave model of light, find the amplitude of the electric field (in N/C) and the magnetic field (in T) at the point 3m from the laser output, along the direction of the beam.

Please show steps and any relevant equations.

Thanks =)

Explanation / Answer

Here ,

Power , P = 5 mW

intensity of wave , I = 5 *10^-3/(4pi * (0.001)^2)

I = 397.9 W/m^2

for the amplitude of the electric field is E

I = 0.5 * E^2/(c * u0)

397.9 = 0.5 * E^2/(3 *10^8 * 4pi *10^-7)

solving for E

E = 547.7 N/C

the amplitude of electric field is 547.7 N/C

amplitude of magnetic field = E/c

amplitude of magnetic field = 547.7/(3 *10^8)

amplitude of magnetic field = 1.83 *10^-6 T

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