The critical angle of a medium with respect to air is $45^o$. The refractive index of the medium is

Which of the following is not due to total internal reflection?

Explain the use of optical fibre in the medical field.

What is the least radius through which an optical fiber of core diameter $0.05 \, mm$ may be bent (as shown in figure) without serious loss of light (in $, mm$)? The refractive index of the core is $1.6$ and that of cladding is $1.5$.

$A$ ray of light travelling in a transparent medium of refractive index $\mu$ falls on a surface separating the medium from air at an angle of incidence of $45^o$. For which of the following values of $\mu$ can the ray undergo total internal reflection?

Assertion : In optical fibre,the diameter of the core is kept small.
Reason : This smaller diameter of the core ensures that the fibre should have incident angle more than the critical angle required for total internal reflection.