Calculate the critical angle for a glass air interface, if a ray of light incident in air on the surface is deviated through `15^@`, when its angle of incidence is `40^@`.

Explanation

To calculate the critical angle for a glass-air interface given the deviation of a ray of light, we can follow these steps:

### Step 1: Understand the Problem
We have a ray of light incident from air into glass. The angle of incidence (i) is given as 40°, and the ray is deviated by 15°. We need to find the critical angle (C) for the glass-air interface.

### Step 2: Calculate the Angle of Refraction
The deviation (D) is defined as the difference between the angle of incidence (i) and the angle of refraction (r):
\[ D = i - r \]
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