$A$ light ray traveling in a glass medium is incident on a glass-air interface at an angle of incidence $\theta$. The reflected $(R)$ and transmitted $(T)$ intensities,both as functions of $\theta$,are plotted. The correct sketch is:

The velocity of light in a medium is half its velocity in air. If a ray of light emerges from such a medium into air,the angle of incidence,at which it will be totally internally reflected,is ......... $^o$

$A$ light ray falls on a square glass slab as shown in the diagram. The index of refraction of the glass,if total internal reflection is to occur at the vertical face,is equal to

$A$ diver in a swimming pool wants to signal his distress to a person lying on the edge of the pool by flashing his waterproof flashlight. In which direction should he direct the beam?

$PQR$ is a right-angled prism with other angles as $60^o$ and $30^o$. The refractive index of the prism is $1.5$. $PQ$ has a thin layer of liquid. Light falls normally on the face $PR$. For total internal reflection at the face $PQ$,the maximum refractive index of the liquid is

The critical angle for a medium is $60^o$. The refractive index of the medium is: