मानक स्थितियों में निर्वात के सापेक्ष वायु का अपवर्तनांक लगभग किसके बराबर होता है?

In a concave lens, a ray of light emanating from the object parallel to the principal axis of the lens, after refraction:

A ray of light incident at an angle θ on face AB of a prism of refractive index 1.5 emerges normally from its face AC. If the angle of the prism is 5°, the angle of incidence θ should be nearly: