Question

A prism has a refracting angle of 60${}^{\circ }$. When placed in the position of minimum deviation, it produces a deviation of 30${}^{\circ }$. The angle of incidence is:

• A. 30${}^{\circ }$
• B. 45${}^{\circ }$
• C. 15${}^{\circ }$
• D. 60${}^{\circ }$

Answer 1

Answer: (B)

45${}^{\circ }$

$\mu =\frac{sini}{sinr}=\frac{sin\left(\frac{\delta +A}{2}\right)}{sin\left(A/2\right)}$

$r=A/2$

$\frac{sin\left(i\right)}{sin\left(A/2\right)}=\frac{sin\left(\frac{\delta +A}{2}\right)}{sin\left(A/2\right)}$

$i=(\delta +A)/2$

$=\frac{30+60}{2}$

$={45}^{\circ }$