Total internal reflection may occur when light travels from _____

Options

A. vacuum to air
B. water to glass
C. air to glass
D. glass to water

Answer

To determine when total internal reflection (TIR) may occur, we need to understand the conditions necessary for TIR to take place. Here’s a step-by-step solution to the question:

### Step 1: Understand Total Internal Reflection
Total internal reflection occurs when light travels from a denser medium to a rarer medium. There are two key conditions:
1. The light must be traveling from a denser medium to a rarer medium.
2. The angle of incidence must be greater than the critical angle.

### Step 2: Identify the Mediums
We are given the following options:
- Vacuum to air
- Water to glass
- Air to glass
- Glass to water

### Step 3: Determine the Refractive Indices
To identify which mediums are denser or rarer, we need to know their refractive indices:
- Vacuum: Refractive index ≈ 1.0 (rarest)
- Air: Refractive index ≈ 1.0003 (rarer than water and glass)
- Water: Refractive index ≈ 1.333 (denser than air)
- Glass: Refractive index ≈ 1.517 (denser than both air and water)

### Step 4: Analyze Each Option
1. **Vacuum to Air**: Light is moving from a rarer medium (vacuum) to a denser medium (air). This does not satisfy the condition for TIR.

2. **Water to Glass**: Light is moving from a rarer medium (water) to a denser medium (glass). This does not satisfy the condition for TIR.

3. **Air to Glass**: Light is moving from a rarer medium (air) to a denser medium (glass). This does not satisfy the condition for TIR.

4. **Glass to Water**: Light is moving from a denser medium (glass) to a rarer medium (water). This satisfies the condition for TIR, provided the angle of incidence is greater than the critical angle.

### Step 5: Conclusion
Based on the analysis, the correct answer is that total internal reflection may occur when light travels from **glass to water**.

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