Question

Swarali observed that the light bent away from the normal, while travelling from

dense medium to rarer medium. When Swarali increased the values of angle of

incidence (i), the values of angle of refraction (r) went on increasing. But at a

certain angle of incidence, the light rays returned into the dense medium.

So, Swarali has some questions. Answer them –

a) Name this certain value of ‘i ’. What is the value of ‘r’ at that time ?

b) Name this process of returning of light in dense medium. Explain the process.

Answer 1

a] When the angle of refraction reaches an absolute value of 90 degree both the angle of incidence and the angle of refraction keep on increasing. This value is known as the absolute value.

b] This process is known as total internal reflection. When light reaches a point where its angle of refraction reaches its absolute value it further reflects out. This process is common in rainbow formation or when light travels through a water droplet. Please check the answer to be sure.

Thank you.

Answer 2

I. When the angle of refraction is equal to 90 then the angle of i become critical angle. When we increases the critical angle i.e. I the refracted Ray bends further away from normal and the light bends back in Denser medium.

The value of i is greater than critical angle and value of r is greater than 90.

2.this is called as total internal reflection