Question

A ray of light is normally incident on one face of an equilateral prism. Trace the course of the ray through the prism and emergingfrom it.

Answer 1

Incident ray falls on one side of prism and emerges out from from another side as shown in figure

Answer 2

Answer:

(a) If the incident ray normal to prism then angle of incidence is $0^{o}$.

b) In this case the angle of refraction from the first face $r1 = 0^{o}$.

(c) As the prism is equilateral so $A = 60^{0}$and $r1 = 0^{o} .$ So at the second face of the prism, the angle of incidence will be $60^{0}$.

(d) No the light will not suffer minimum deviation.

Explanation:

(a) The angle of incidence on the first face of the prism when a ray of light is normally incident is 0°.

(b) The angle of refraction from the first face of the prism r1 = 0° as the angle of refraction of a normally incident ray is always 0°.

(c) As the prism is equilateral therefore A = 60°.

Given, r1 = 0°.

Hence, taking into consideration the two conditions we get,

the angle of incidence at the second face of the prism, equal to 60°.

(d) No, the light ray will not suffer minimum deviation as the angle of incidence is 0°.

The ray will not undergo any deviation at the first surface since it is incident normally.

Using external angle theorem,

$\angle ADE+\angle DAE=\angle DEC\\90^{0} +60^{0} =90^{0} +r\\r=60^{0}$