$A$ step index fibre has a relative refractive index difference of $0.88\%$. What is the critical angle at the core-cladding interface in degrees?

The critical angle of a medium for a specific wavelength,if the medium has relative permittivity $3$ and relative permeability $\frac{4}{3}$ for this wavelength,will be.....$^o$

$A$ cylindrical transparent rod of refractive index $\mu = \frac{2}{\sqrt{3}}$ is surrounded by air. $A$ light ray is incident at the midpoint of one end of the rod as shown in the figure. The angle of incidence $\theta$ for which the light ray undergoes total internal reflection at the side wall of the rod is:

For a ray of light,the critical angle is minimum,when it travels from

$A$ ray of light travels from a denser medium to a rarer medium. The reflected and the refracted rays are perpendicular to each other. If '$i$' and '$r_1$' are the angle of incidence and angle of refraction respectively and '$C$' is the critical angle,then the angle of incidence is

$A$ beam of light is incident from air on the surface of a liquid. The angle of incidence is $\theta$ and the angle of refraction is $\alpha$. If the critical angle for the liquid when surrounded by air is $\theta_c$,then $\sin \theta_c$ is: