Fill in the blanks:
Q: Total internal reflection occurs only when a ray of light passes from a _____medium to a ____medium.

Answer

To solve the question, we need to understand the concept of total internal reflection and the conditions under which it occurs.

### Step-by-Step Solution:

1. **Understanding Total Internal Reflection**: Total internal reflection is a phenomenon that occurs when a light ray traveling in a denser medium hits the boundary of a rarer medium at an angle greater than the critical angle.

2. **Identifying the Mediums**:
- A **denser medium** is one in which light travels slower (e.g., glass, water).
- A **rarer medium** is one in which light travels faster (e.g., air).

3. **Filling in the Blanks**:
- The first blank should be filled with "denser" because the light ray must start in a denser medium.
- The second blank should be filled with "rarer" because the light ray must be passing into a rarer medium.

4. **Final Answer**: Total internal reflection occurs only when a ray of light passes from a **denser** medium to a **rarer** medium.