Question

An equilateral prism deviates a ray through ${45}^{\circ }$ for two angle of incidences differing by ${20}^{\circ }$. The angle of incidences are

• A. ${60}^{\circ }$ and ${40}^{\circ }$
• B. ${50}^{\circ }$ and ${40}^{\circ }$
• C. ${62}^{\circ }{30}^{\prime }$ and ${42}^{\circ }{30}^{\prime }$
• D. ${60}^{\circ }{30}^{\prime }$ and ${40}^{\circ }{30}^{\prime }$

Answer 1

The correct option is C ${62}^{\circ }{30}^{\prime }$ and ${42}^{\circ }{30}^{\prime }$

Angle of deviation $d=i+e-A$

$45+60=i+e$

When the emergent ray acts as incident ray,the devation is same.

$l=i+20$

$2i={85}^{\circ }$

$i={42}^{\circ }{30}^{\prime }$

$l={62}^{\circ }{30}^{\prime }$