Which of the following is not due to total internal reflection ?

Options

A. Difference between apparent and real depth of a pond
B. Mirage on hot summer days
C. Brilliance of diamond
D. Working of optical fiber

Answer

To determine which of the following phenomena is not due to total internal reflection, we need to analyze the options provided in the question.

1. **Understanding Total Internal Reflection**:
Total internal reflection occurs when a wave (like light) hits a boundary between two media at an angle greater than the critical angle, causing all the light to be reflected back into the medium instead of refracting into the second medium. This phenomenon is responsible for several optical effects.

2. **Analyzing the Options**:
- **Option 1**: Apparent depth in a pond - This phenomenon is due to refraction, not total internal reflection. When light travels from water to air, it bends, making the object appear shallower than it actually is.
- **Option 2**: Brilliance of diamonds - This is due to total internal reflection. Diamonds have a high refractive index, and when light enters them, it reflects internally, enhancing their brilliance.
- **Option 3**: Working of optical fibers - Optical fibers utilize total internal reflection to transmit light signals over long distances without significant loss.
- **Option 4**: Rainbow formation - This is primarily due to refraction and dispersion of light, but total internal reflection can also play a role in the formation of secondary rainbows.

3. **Conclusion**:
Based on the analysis, the phenomenon that is not due to total internal reflection is the apparent depth in a pond. Therefore, the correct answer is the first option.

### Step-by-Step Solution:
1. Define total internal reflection and its conditions.
2. Identify the options provided in the question.
3. Analyze each option to determine if it is due to total internal reflection or not.
4. Conclude that the apparent depth in a pond is due to refraction, not total internal reflection.