Question

A typical green laser pointer, operating at a wavelength of 532 nm, delivers an average power of 5 mW in a circular beam of 1 mm radius. What is the rms magnetic field in this beam?

3.48E-5 T

6.81E-7 T

9.18E-4 T

7.35E-6 T

2.58E-6 T

Answer 1

We know that Intensity of laser pointer will be given by:

Intensity = Power/Area

Average power of laser pointer = 5 mW = 5*10^-3 W

Area of circular beam = pi*r^2 = pi*(1*10^-3)^2 = pi*10^-6 m^2

So,

I = 5*10^-3/(pi*10^-6) = 1591.55 W/m^2

Now relation between magnetic field and average intensity is given by:

I_avg = E_rms^2/(*c) = (c*B_rms)^2/(*c)

I_avg = c*B_rms^2/

B_rms = sqrt [*I_avg/c]

B_rms = sqrt (4*pi*10^-7*1591.55/(3*10^8))

B_rms = 2.58*10^-6 T

Correct option is E.