Question

A 12.7 mW laser puts out a narrow beam 1.50 mm in diameter. What
are the average (rms) values of *E* and *B* in the
beam?

E = |
______V/m |

B = |
_______T |

Answer #1

For e/m waves, E and B are at right angles; so, sin theta = 1
Therefore E cross B becomes EB. Also, E=Bc so that B=E/c

Diamener of beam: 1.5mm

Radius of beam = 1.5mm/2 = 0.75mm

Radius of beam =0.75 x 10^-3 m

Area of beam = pi x (0.75 x 10^-3) m^2

Area of beam = 1.76625 x 10^-6 m^2

S = Watts per unit area = 12.7 x 10^-3/1.76625 x 10^-6

S = 7190.38 Watts/m^2

S=(E^2)/c x uo

Giving:-

E= Root[7190.38 x 3 x 10^8 x 4 x pi x 10^-7]

E=Root[7190.38 x 377]

E=Root[2 x 10^6]

E = 1646.4Vm-1

Emax = 1646.4 x root[2] = 2328.42Vm-1

Emax = 2328.42Vm-1

B = E/c

B = 2328/3x10^8

B = 7.76 x 10^6 T

B = 7.76uT

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