$A$ ray of light from a denser medium strikes a rarer medium. The angle of reflection is $r$ and that of refraction is $r'$. The reflected and refracted rays make an angle of $90^{\circ}$ with each other. The critical angle will be

Assertion: Critical angle is minimum for violet colour.
Reason: Because critical angle $\theta_c = \sin^{-1} \left( \frac{1}{\mu} \right)$ and $\mu \propto \frac{1}{\lambda}$.

At the interface between two materials having refractive indices $n_1$ and $n_2$,the critical angle for reflection of an electromagnetic wave is $\theta_{1C}$. The $n_2$ material is replaced by another material having refractive index $n_3$,such that the critical angle at the interface between $n_1$ and $n_3$ materials is $\theta_{2C}$. If $n_3 > n_2 > n_1$,$\frac{n_2}{n_3} = \frac{2}{5}$,and $\sin \theta_{2C} - \sin \theta_{1C} = \frac{1}{2}$,then $\theta_{1C}$ is:

It is found that all electromagnetic signals sent from $A$ towards $B$ reach point $C$. The speed of electromagnetic signals in glass can not be

$A$ prism has a refractive index of $1.5$. If a light ray undergoes total internal reflection at the interface with a liquid,what is the maximum possible refractive index of the liquid? (Refer to the provided diagram for geometry).

The figure shows a transparent block of side lengths $a$ and $a$. The third dimension of the block is negligible. $A$ point source $S$,which can emit light in all directions,can move inside the block. It is desired that no light from $S$ should pass through the segment $AB$. The region in which $S$ must be present to satisfy this condition is shown by the shaded region. Choose the correct option.