$A$ ray is incident from a medium of refractive index $2$ into a medium of refractive index $1$. The critical angle is (in $^{\circ}$)

$A$ point source $S$ is placed at the bottom of different layers as shown in the figure. The refractive index of the bottom-most layer is $\mu_0$. The refractive index of any other upper layer is $\mu(n) = \mu_0 - \frac{\mu_0}{4n - 18}$,where $n = 1, 2, \dots$. $A$ ray of light with an angle of incidence $i$ slightly more than $30^\circ$ starts from the source $S$. Total internal reflection takes place at the upper surface of a layer having $n$ equal to

$A$ beam of light consists of red,green,and blue colors. It is incident on the $AB$ face of a right-angled prism as shown in the figure. The refractive indices for red,green,and blue colors are $1.39$,$1.44$,and $1.47$ respectively. What will a person see when looking at the $AC$ surface of the prism?

If the refractive index of water is $\frac{4}{3}$ and that of a given glass slab immersed in it is $\frac{5}{3}$,the value of the critical angle for a ray of light tending to go from glass to water is:

The radius of the light circle observed by a fish at a depth of $12 \ m$ is (refractive index of water $\mu = 4/3$):

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