A laser beam enters a 19.5 cm thick glass window at an angle of 63.0 degree from

Question

A laser beam enters a 19.5 cm thick glass window at an angle of 63.0 degree from the normal. The index of refraction of the glass is 1.48. At what angle from the normal does the beam travel through the glass? 3.70 times 10^1 deg How long does it take the beam to pass through the plate? First you have to calculate the distance that the beam travels through the plate. In order to calculate the time, you need the velocity. The velocity of the beam in the medium is related to the velocity of the speed of light in air (vacuum) via the index of refraction.

Explanation / Answer

using Snell's law

n1*sin(i) = n2*sin(r)

1*sin(63) = 1.48*sin(r)

sin(r) = sin(63)/1.48 = 0.602

r = sin^(-1)(0.602) = 37 degrees

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distnace travelled by the light in glass is x

then

cos(r) = t/x

cos(37) = 19.5/x

x = 24.42 m

speed of light in glass is v = c/n

v= (3*10^8)/(1.48)

v = 2.02*10^8 m/sec

then time taken is t = x/v = 0.2442 /(2.02*10^8)

t = 1.208*10^-9 sec

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