Question

A parallel beam of monochromatic light is incident on one face of an equilateral prism the angle of incidence being ${55}^{\circ }$. The angle of emergence of the beam from the other face is ${46}^{\circ }$. The angle of minimum deviation is :

• A. $<{41}^{\circ }$
• B. equal to ${41}^{\circ }$
• C. $>{41}^{\circ }$
• D. $\ge {41}^{\circ }$

Answer 1

Answer: (A)

$<{41}^{\circ }$

By the hypothesis, we know that

$A+\delta =i_1+i_2$

$⟹\delta =i_1+i_2-A$

$⟹\delta ={55}^0+{46}^0-{60}^0={41}^0$

But

${\delta }_m<\delta$

So,

${\delta }_m<{41}^0$