A ray of light is incident normally on one of the refracting surface of an equilateral prism.

Question

 If the refractive index of the material of the prism is 1.5 then:

• The emergent ray is deviated by 30⁰
• The emergent ray is deviated by 60⁰
• The emergent ray just graces the second reflecting surface
• the ray undergoes total internal reflection at the second refracting surface
• The ray emerges normally from the second refracting surface

Answer 1

the ray undergoes total internal reflection at the second refracting surface.

The ray of light goes into the prism without deviation and is incident on the opposite face of the prism. It undergoes total internal reflection.

Comments

why you down voted, answer is correct

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answer is option A

Answer 2

The correct option is (d) as explained below:

The ray PQ incident normally on the face AB of the prism proceeds undeviated through the prism and strikes the face AC at the point R, as shown in the adjoining figure. From the right angled triangle AQR it is clear that angle QRA = 30º. Therefore, it follows that the angle of incidence QRN at the face AC is 60º. Since this is greater than the critical angle (which is slightly less than 42º for the material of refractive index 1.5), the ray is totally reflected along RS as shown in the figure.

[You may calculate the critical angle using the equation,

n = 1/sinC where n is the refractive index and C is the critical angle.

Therefore sinC = 1/1.5 = 0.66667 and C = sin–1(0.66667) = 41.8º]