(c) In an optical fibre, if n 1 and n 2 are the refractive indices of the core and cladding, then which among the following, would be a correct equation?
(i) n 1 < n 2
(ii) n 1 = n 2
(iii) n 1 << n 2
(iv) n 1 > n 2
Answer
Optical Fibres work on the principle of total internal reflection .
The main conditions for total internal reflection are:
- Light should travel from denser to rarer medium.
- Angle of incidence should be greater than critical angle
Therefore,
The refractive index of the core is greater than the refractive index of the cladding.
So the correct answer is (iv)
