Question

The expected graphical representation of the variation of angle of deviation ${}^{\prime }{\delta }^{\prime }$ with angle of incidence ${}^{\prime }{i}^{\prime }$ in a prism is :

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

We know that the angle of deviation depends upon the angle of incidence as
$\delta =(i+e-A)$, where, $i$ is the angle of incidence, $e$ is the angle of emergence and $A$ is the angle of prism.
When the angle of incidence and angle of emergence are equal, then the angle of deviation will be minimum. Thus, it can be called a minimum deviation.
The deviation produced by the prism is maximum when either the angle of incidence or angle of emergence is ${90}^{\circ }$. This is known as the grazing angle. At this condition, either incident ray or emergent ray will graze along the surface of the prism.
For any other angle of deviations except the angle of minimum deviation, the angle of incidence and angle of emergence can’t be interchanged. That means it has specific values. From the relation between the angle of incidence and angle of deviation, we can say that it is not a linear relationship.
If we determine experimentally, the angles of deviation corresponding to different angles of incidence and then plot ${}^{\prime }{i}^{\prime }$ (on x-axis) and ${}^{\prime }{\delta }^{\prime }$ (on y-axis) we get a curve as shown in figure.

Hence, option (b) is correct.