Which is true for total internal reflection?

Options

A. Light travels from rarer to denser medium
B. Light travels from denser to rarer medium
C. Independent of the optical densities of two medium
D. Takes place in the same medium

Explanation

### Step-by-Step Solution:

1. **Understanding the Concept of Total Internal Reflection**:
Total internal reflection occurs when light travels from a denser medium to a rarer medium and strikes the interface at an angle greater than the critical angle.

2. **Identifying the Mediums**:
- Let’s denote the two mediums involved:
- Medium 1 (denser medium) has a refractive index \( \mu_2 \).
- Medium 2 (rarer medium) has a refractive index \( \mu_1 \).
- Here, \( \mu_2 > \mu_1 \).

3. **Incident Angle and Critical Angle**:
- When light travels from the denser medium (medium 1) to the rarer medium (medium 2), it can be refracted.
- If the angle of incidence \( i \) is less than the critical angle \( C \), the light will refract into the rarer medium.
- If the angle of incidence \( i \) is equal to the critical angle \( C \), the light will refract along the boundary.
- If the angle of incidence \( i \) is greater than the critical angle \( C \), total internal reflection occurs, and the light does not pass into the rarer medium but reflects back into the denser medium.

4. **Condition for Total Internal Reflection**:
- The condition for total internal reflection is that the light must be moving from a denser medium to a rarer medium, and the angle of incidence must exceed the critical angle.

5. **Conclusion**:
- Therefore, the statement that is true for total internal reflection is that it occurs when light travels from a denser medium to a rarer medium and the angle of incidence is greater than the critical angle.