The table below gives refractive inidices of some substances with respect to air.

Substance	Refractive Index (μ)
Water	1.33
Turpentine	1.47
Glass	1.58
Diamond	2.41

(a) Which medium will have the lowest critical angle and which will have highest critical angle with respect to air.

(b) If the temperature of all the substances is raised by 30^o C, what will happen to their critical angle?

(a) Diamond has lowest critical angle and water has highest critical angle.

(b) If the temperature of all the substance is raised by 30^o C then the critical angle of the all the media will increase.

Reason :

(a) As the relation between critical angle and refractive index of a medium is given by, $\text{sin C} = \dfrac {1}{$a\text{μ}{medium}}

where ${}_a{\text{μ}}_{medium}$a\text{μ}{medium} is the refractive index of the given medium with respect to air

From above relation it is clear that critical angle (C) has inverse relation with refractive index (${}_a{\text{μ}}_{medium}$a\text{μ}{medium}) so lowest C is the one with highest value of ${}_a{\text{μ}}_{medium}$a\text{μ}{medium} and similarly highest C value corresponds to lowest ${}_a{\text{μ}}_{medium}$a\text{μ}{medium}.

(b) On increasing the temperature of a medium, it's refractive index decreases, therefore the critical angle increases with the increase in temperature.