The phenomenon by which light travels in an optical fibre is

On which principle does an optical fiber work?

The graph between the sine of the angle of refraction $(\sin r)$ in medium $2$ and the sine of the angle of incidence $(\sin i)$ in medium $1$ is shown below. Based on this,which of the following statements is correct? (Given: $\tan 36^o \approx \frac{3}{4}$)

$A$ diver looking up through the water sees the outside world contained in a circular horizon. The refractive index of water is $\frac{4}{3}$,and the diver's eyes are $15 \, cm$ below the surface of water. Then the radius of the circle is

$A$ rod of glass $(\mu = 1.5)$ with a square cross-section is bent into the shape shown in the figure. $A$ parallel beam of light falls on the plane flat surface $A$ as shown. If $d$ is the width of a side and $R$ is the radius of the inner circular arc,what is the maximum value of $\frac{d}{R}$ such that the light entering the glass slab through surface $A$ emerges from the glass through $B$?

The critical angle for light traveling from medium $(i)$ to medium $(ii)$ is $\theta$. If the speed of light in medium $(i)$ is $v$,then the speed of light in medium $(ii)$ is: