Physics - Geometrical Optics Question with Solution | TestHub

We know that angle of deviation depend upon the angle of incidence. If we determine experimentally the angle of deviation corresponding to different angles of incidence then and then plot $i$ (on $x$-axis) and $\delta$ (on $y$-axis), we get a curve as shown in figure.

Clearly, if angle of incidence is gradually increased from a small value, the angle of deviation first decreases, becomes minimum for a particular angle of incidence and then begins to increase.