A ray of light incident at an angle on a refracting face of a prism emerges from the other face normally. If the angle of the prism is 5° and the prism is made of a material of refractive index 1.5, the angle of incidence is
Let the light enter the prism at B making an angle 
. It refracts away from the normal. Let it strike the other face of the prism at C. It is given that it comes out normally. This is only possible if it is incident at the face normally. Hence, 
Note that it is given that 
.
Now, the sum of angles in a triangle is 180°. In ΔABC,
Now, we use Snell’s law on the interface AB
where nair is the refractive index of air, nglass is the refractive index of glass (=1.5), θi is the angle of incidence and θr is the angle of refraction.
Substituting the appropriate values, we get
The only option with the value 7.5° is (a). Hence, option (a) is correct.