A prism is made of glass of unknown refractive index. A parallel beam of light is incident on the face of the prism. The angle of minimum deviation is measured to be $40^\circ.$ What is the refractive index of the material of the prism?
(The refracting angle of the prism is $60^\circ$)
1. $1.43$
2. $1.33$
3. $1.50$
4. $1.53$

At what angle should a ray of light be incident on the face of a prism of refracting angle $60^{\circ}$ so that it just suffers total internal reflection at the other face? The refractive index of the material of the prism is $1.524$.
1. $29.75^\circ$
2.$19^\circ$
3.$17.23^\circ$
4.$19.57^\circ$