Part Ill: Total Internal Reflection 1. Find the critical angle. With the curved side of the lens facing the incident ray rotate the ray table again. You should find an angle past which the transmitted ray disappears. Record the value of the incident angle at which this happens. This is called the critical angle. critical angle Starting from Snell\'s Law, derive an expression for the critical angle. Where does the refracted ray disappear and why? 2. Solution 2. n 1 = index of refraction for the medium where the light incident n 2 = index of refraction for the medium where the light is supposed to refract necessary condition for total internal reflection is that n 2 <n 1 i = angle of incidence r = angle of refraction using snell\'s law n 1 Sini = n 2 Sinr for total internal reflection , i = C r = 90 hence n 1 SinC = n 2 C = Sin -1 (n 2 /n 1 ) at critical angle, the ray does not refract instead , it gets reflected back When a ray is refracted from denser medium to rarer medium it makes greater angle of refraction than incidence meaning it moves away from the normal. If we gradually increase the incident angle, at one point the refraction angle will become 90 degree means the ray in not going in to the rarer medium inster it moves in the direction perpendicular to the rarer medium, this angle of incidence is called critical angle. And if we further increase the incidence angle then the ray moves back from same medium and this phenomenon is called Total Ineternal reflection. .

1. Part Ill: Total Internal Reflection 1. Find the critical angle. With the curved side of the lens
facing the incident ray rotate the ray table again. You should find an angle past which the
transmitted ray disappears. Record the value of the incident angle at which this happens. This is
called the critical angle. critical angle Starting from Snell's Law, derive an expression for the
critical angle. Where does the refracted ray disappear and why? 2.
Solution
2.
n 1 = index of refraction for the medium where the light incident
n 2 = index of refraction for the medium where the light is supposed to refract
necessary condition for total internal reflection is that n 2 <n 1
i = angle of incidence
r = angle of refraction
using snell's law
n 1 Sini = n 2 Sinr
for total internal reflection , i = C
r = 90
hence
n 1 SinC = n 2
C = Sin -1 (n 2 /n 1 )
at critical angle, the ray does not refract instead , it gets reflected back

2. When a ray is refracted from denser medium to rarer medium it makes greater angle of
refraction than incidence meaning it moves away from the normal. If we gradually increase
the incident angle, at one point the refraction angle will become 90 degree means the ray in
not going in to the rarer medium inster it moves in the direction perpendicular to the rarer
medium, this angle of incidence is called critical angle. And if we further increase the
incidence angle then the ray moves back from same medium and this phenomenon is called
Total Ineternal reflection.