Question Details

Find the value of the angle of emergence from the prism. Refractive index of the glass is square root of 3.

Options

A

60⁰

B

30⁰

C

45⁰

D

90⁰

Correct Answer :

60⁰

Solution :

The correct answer is 60⁰.

Step-by-Step Derivation:

1. Identify the angles of the prism:
From the given image, the prism is a right-angled triangle.
The angle at the bottom-left vertex is 90°, and the angle at the bottom-right vertex is 60°.
Therefore, the angle at the top vertex (let's call it A) is:
A=180°-(90°+60°)=30°

2. Determine the path of the light ray inside the prism:
The incident light ray enters normally (perpendicularly) to the hypotenuse face of the prism.
Since the angle of incidence at this first surface is 0°, the ray passes straight into the prism without any deviation.

3. Calculate the angle of incidence at the vertical face:
Let P be the point of entry on the hypotenuse, and Q be the point where the ray hits the vertical face.
In the right-angled triangle formed by the top vertex A, the entry point P, and the point Q on the vertical face (ΔAPQ):
The angle APQ=90° (since the ray enters normally).
The angle at the top vertex is PAQ=30°.
Therefore, the third angle in the triangle, AQP, is:
AQP=180°-(90°+30°)=60°
The normal to the vertical face is perpendicular (90°) to that face. Thus, the angle of incidence (i) on the vertical face is:
i=90°-60°=30°

4. Apply Snell's Law to find the angle of emergence (e):
According to Snell's Law at the interface of the vertical face:
μ·sin(i)=μair·sin(e)
Where:
- The refractive index of glass is μ=3
- The refractive index of air is μair=1
- The angle of incidence is i=30°
Substituting these values:
3·sin(30°)=1·sin(e)
Since sin(30°)=12:
sin(e)=32
Taking the inverse sine:
e=60°

Thus, the angle of emergence from the prism is 60⁰.

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