The critical angle of light passing from glass to air is minimum for which color of light?

On which principle does an optical fiber work?

In an optical fibre, is the refractive index of the core greater than that of the cladding, or smaller?

$A$ light ray is incident perpendicularly to one face of a $90^{\circ}$ prism and is totally internally reflected at the glass-air interface. If the angle of incidence at the interface is $45^{\circ}$,we conclude that the refractive index $n$ is:

Total internal reflection of a ray of light is possible when the ($i_c$ = critical angle,$i$ = angle of incidence)

$A$ ray of light refracts from medium $1$ into a thin layer of medium $2$, crosses the layer, and is incident at the critical angle on the interface between medium $2$ and $3$ as shown in the figure. If the angle of incidence of the ray is $\theta$, the value of $\theta$ is