A light ray is incident fromt a denser medium on the boundary separating it from a rarer medium at an angle of incidence equal to the critical angle. What is the angle of refraction for the ray ?

Answer

To solve the problem, we will follow these steps:

### Step 1: Understand the concept of critical angle
The critical angle is defined as the angle of incidence in the denser medium at which the angle of refraction in the rarer medium is 90 degrees. This occurs when light travels from a denser medium (higher refractive index) to a rarer medium (lower refractive index).

### Step 2: Identify the given information
We are given:
- The light ray is incident from a denser medium to a rarer medium.
- The angle of incidence (i) is equal to the critical angle (C).

### Step 3: Apply the definition of critical angle
According to the definition, when the angle of incidence is equal to the critical angle, the angle of refraction (r) will be 90 degrees. This means that the refracted ray will travel along the boundary between the two media.

### Step 4: State the conclusion
Since the angle of incidence is equal to the critical angle, the angle of refraction will be:
- r = 90 degrees.

### Final Answer
The angle of refraction for the ray is 90 degrees.

---