Question

In an equilateral prism if the angle of incidence for minimum angle of deviation is ${35}^0$ then what is the minimum angle of deviation?

• A. ${30}^0$
• B. ${20}^0$
• C. ${10}^0$
• D. ${45}^0$

Answer 1

The correct option is C ${10}^0$

Given: In an equilateral prism if the angle of incidence for minimum angle of deviation is ${35}^{\circ }$

To find the minimum angle of deviation.

Solution:

When the angle of incidence is such that the angle of deviation is minimum, then

$i=\frac{A+{\delta }_m}{2}$

where $i$ is the angle of incidence,

$A$ is the angle of the prism, and,

${\delta }_m$ is the angle of minimum deviation.

And in equilateral prism, $A={60}^{\circ }$

Therefore,

$⟹35\times 2=60+{\delta }_m⟹{\delta }_m=70-60={10}^{\circ }$

is the minimum angle of deviation.