A beam of laser light with wavelength 602 nm is directed through a slab of glass

Question

A beam of laser light with wavelength 602 nm is directed through a slab of glass having index of refraction 1.50.

a) For what minimum incident angle would a ray of light undergo total internal reflection?   

b) If a layer of water is placed over the glass, what is the minimum angle of incidence on the glass-water interface that will result in total internal reflection at the water-air interface? (The beam of light is directed upward through the slab of glass, through the layer of water, and experiences total internal reflection at the water-air interface on top.)    

Explanation / Answer

Applying Snell's law at the air glass interface,

refractive index is n = 1.5

n sinA = nb * sin 90

(1.5)* sin A = 1

A = 41.81 deg

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2)

The refractive index of the water is n2 = 1.33

Applying Snell's law at the air water interface,

n2 sin A' = sin90

(1.33)* sini' = 1

i' = 48.75o

The ray from the glass is refracted at r = i' = 48.75o

Applying Snell's law at the glass water interface,

n1 sin B = n2* sin48.75

(1.5)* sin B = (1.33)* sin48.75

B = 41.81 deg

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