5. Assume the helium-neon lasers commonly used in physics laboratories have powe

Question

5. Assume the helium-neon lasers commonly used in physics laboratories have power of 0.250 mWw (a) If such a laser beam is projected onto a circular spot what is its intensity? 1.00 mm in diameter. (e) Find the peak magnetic field strength (Bu). (c-3.00x 101 mis:-4x x 10" Tm/A) (c) Find the peak electric field strength (Eo). The optical fiber is made of flint glass with index of refraction of 1.66. (a) What is the speed of light in such optical fiber? 6. What is the average time for signal to cross the Atlantic Ocean (3400 km) in such optical cable? (b) 7. Find the critical angle for the total internal reflection in a Plexiglas when (nair 1.00; nplesigla -1.51) (a) the plexiglas is in air 1.33) (b) the plexiglas is immersed in water. (oat

Explanation / Answer

5)

given,

Power, P=0.25 mW =0.25*10^-3 W

diameter, d=1mm

radius, r=0.5*10^-3 m

a)

intensity, I=P/A

=(0.25*10^-3)/(pi*(0.5*10^-3)^2)

=318.31 W/m^2

b)

I=1/(2C*uo)*Eo^2

I=1/(2*uo)*C*Bo^2

318.31=1/(2*4pi*10^-7)*3*10^8*Bo^2

===> Bo=1.633*10^-6 T

c)

use,

Eo=c*Bo

Eo=3*10^8*1.633*10^-6

==> elecric field, Eo=489.9 v/m

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