calculate the angle of refraction of light incident on water surface at an angle of 52 degree take mu =4/3
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Critical Angle and Total Internal Reflection
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Total Internal Reflection
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Total Internal Reflection
When a ray of light AO passes from an optically denser medium to a rarer medium, at the interface XY, it is partly reflected back into the same medium along OB and partly refracted into the rarer medium along OC as shown in figure.
If the angle of incidence is gradually increased, the angle of refraction r will also gradually increase and at a certain stage r becomes 90o. Now the refracted ray OC is bent so much away from the normal and it grazes the surface of separation of two media.The angle of incidence in the denser medium at which the refracted ray just grazes the surface of separation is called the critical angle c of the denser medium.
If i is increased further, refraction is not possible and the incident ray is totally reflected into the same medium itself. This is called totalinternal reflection.

If µd is the refractive index of the denser medium then, from Snell’s Law, the refractive index of air with respect to the denser medium is given by,
µa/ µd = sin i /sin r
1/ µd = sin i/sin r (Since, µa = 1 for air)
If r = 90o, i = c
sin c/sin 90o = 1/µd
Or, sin c = 1/µd
Or, c = sin-1(1/µd)
If the denser medium is glass, c = sin-1(1/µg)
Table of Content
Total Internal Reflection
Applications
Test your knowledge
Related Resources
Total Internal Reflection
When a ray of light AO passes from an optically denser medium to a rarer medium, at the interface XY, it is partly reflected back into the same medium along OB and partly refracted into the rarer medium along OC as shown in figure.
If the angle of incidence is gradually increased, the angle of refraction r will also gradually increase and at a certain stage r becomes 90o. Now the refracted ray OC is bent so much away from the normal and it grazes the surface of separation of two media.The angle of incidence in the denser medium at which the refracted ray just grazes the surface of separation is called the critical angle c of the denser medium.
If i is increased further, refraction is not possible and the incident ray is totally reflected into the same medium itself. This is called totalinternal reflection.

If µd is the refractive index of the denser medium then, from Snell’s Law, the refractive index of air with respect to the denser medium is given by,
µa/ µd = sin i /sin r
1/ µd = sin i/sin r (Since, µa = 1 for air)
If r = 90o, i = c
sin c/sin 90o = 1/µd
Or, sin c = 1/µd
Or, c = sin-1(1/µd)
If the denser medium is glass, c = sin-1(1/µg)
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