In all optical instruments, we use.

Options

A. ray optics
B. wave optics
C. physical optics
D. none of these

Answer

To solve the question "In all optical instruments, we use," we need to analyze the options provided and determine which one is most applicable to optical instruments.

### Step-by-Step Solution:

1. **Understanding Optical Instruments**: Optical instruments such as microscopes and telescopes are designed to manipulate light to magnify images or observe distant objects.

**Hint**: Consider the fundamental principles behind how these instruments function.

2. **Identifying the Options**: The options given are:
- Ray Optics
- Wave Optics
- Physical Optics
- None of these

**Hint**: Think about the nature of light and how it behaves in different contexts.

3. **Analyzing Ray Optics**: Ray Optics, also known as Geometric Optics, assumes that light travels in straight lines. This assumption is crucial for designing lenses and mirrors in optical instruments.

**Hint**: Recall how light rays are represented in diagrams of lenses and mirrors.

4. **Examining Wave Optics**: Wave Optics deals with the wave nature of light, including phenomena such as interference, diffraction, and polarization. These concepts are not typically applied in the basic functioning of optical instruments.

**Hint**: Consider whether optical instruments rely on the wave nature of light or not.

5. **Considering Physical Optics**: Physical Optics involves the study of light as a wave and includes the quantization of light. However, this approach is not used in the basic design and operation of optical instruments.

**Hint**: Reflect on the differences between treating light as rays versus waves.

6. **Conclusion**: Since optical instruments primarily rely on the straight-line propagation of light, the correct answer is Ray Optics.

**Final Answer**: Ray Optics is used in all optical instruments.