Question

Under what conditions is total internal reflection possible ? Explain it with suitable example . Define critical angle of incidence and obtain an expression for it .​

Answer 1

Answer:

The conditions for total internal reflection are-:

The light rays must be passing from a denser medium to a rarer medium i.e. from glass to air.

The angle of incidence must be greater than critical angle of denser medium.

Critical angle is the angle of incidence in the denser medium corresponding to which the angle of refraction in rarer medium is 90 degree.

The critical angle of glass is 42 degree whereas of water is 49 degree.

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Answer 2

The conditions under which total internal reflection is possible are the light must be traveling from the denser medium to the rarer medium and the angle of incidence must be greater than the critical angle of the medium.

• When light travels from denser medium to rarer medium it gets bent away from the normal.
• If we keep on increasing the angle of incidence, a time will come when the angle of refraction will become 90°.
• The angle of incidence for which the angle of refraction is 90° is known as the critical angle.
• If the angle of incidence goes beyond the angle of refraction the light returns back into the denser medium. This phenomenon is called the total internal reflection.