$A$ 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:

Assertion: The maximum refractive index of the liquid for total internal reflection of the ray passing through the prism as shown in the figure must be $\sqrt 2$.
Reason: Here,the critical angle is $45^o$.

$A$ ray of light travelling in water is incident on its surface open to air. The angle of incidence is $\theta$,which is less than the critical angle. Then there will be

With respect to air,the critical angle in a medium for light of red colour $[{\lambda _1}]$ is $\theta$. Other factors remaining the same,the critical angle for light of yellow colour $[{\lambda _2}]$ will be:

$A$ 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:

Which of the following is used in optical fibres?