Question

A ray of light takes grazing incidence on the first face of a prism and the emergent ray is normal to the $2^{nd}$ face of the prism. If D is angle of deviation then the refracting angle of the prism is equal to

• A. 90${}^{\circ }-2D$
• B. 90${}^{\circ }-D$
• C. 90${}^{\circ }-\frac{D}{2}$
• D. 180${}^{\circ }-2D$

Answer 1

Answer: (B)

90${}^{\circ }-D$

Given, i = 90 , e = 0
For a prism,
D = i + e - A
Thus, A = 90 - D