The wavelengths of light in two liquids $x$ and $y$ are $3500 \, \mathring{A}$ and $7000 \, \mathring{A}$ respectively. The critical angle of $x$ with respect to $y$ is .......... $^o$.

$A$ right-angled glass prism is shown in the figure. $A$ liquid film is in contact with the hypotenuse face. $A$ ray of light incident normally on the face $AB$ will undergo total internal reflection from the hypotenuse face,if the refractive index of the liquid is $\mu_l$ (given $\mu_{\text{glass}} = 3/2$).

In the figure,$ABC$ is the cross-section of a right-angled prism and $BCDE$ is the cross-section of a glass slab. The value of $\theta$ so that light incident normally on the face $AB$ does not cross the face $BC$ is (given $\sin^{-1}(3/5) = 37^o$):

For a light ray to undergo total internal reflection, light must travel from $(i = \text{angle of incidence}, i_C = \text{critical angle})$

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 ......... $^o$

For a ray of light,the critical angle is minimum,when it travels from