A plastic light pipe has an index of refraction of 1.66. For total internal reflection, what...

a)
n1=1.66
refractive indix of air=n2=1
critical angle= asin (n2/n1)
             =asin (1/1.66)
            =37 degree
a)
n1=1.66
refractive indix of water=n2=4/3=1.33
critical angle= asin (n2/n1)
             =asin (1.33/1.66)
            =53.4 degree

a)

in air

1.66*sinC =1*sin90

critical angle C =sin^-1 (1/1.66) =37 degrres

b)

in water

1.66sinC =1.33sin90

C=sin^-1 (1.33/1.66) =53.24 degrees