Which of the following produces a plane wavefront ?

Options

A. Point source
B. Line source
C. Extended source
D. None of these

Answer

To determine which of the following produces a plane wavefront, we need to understand the characteristics of different types of sources of light waves.

### Step-by-Step Solution:

1. **Understanding Wavefronts**:
- A wavefront is a surface over which an oscillation has a constant phase. In simpler terms, it is a surface that connects all points that are in the same phase of a wave.

2. **Types of Sources**:
- **Point Source**: A point source emits waves in all directions, creating spherical wavefronts. This means that the wavefronts are not flat but rather curved.
- **Line Source**: A line source emits waves along a line, producing cylindrical wavefronts. These wavefronts are also not flat.
- **Extended Source**: An extended source can produce various types of wavefronts depending on its shape and size, but typically, it does not produce a plane wavefront.
- **Plane Wave Source**: A plane wavefront is produced when the waves are emitted in parallel lines, typically from a very distant source or a large flat surface.

3. **Examples of Plane Wavefronts**:
- Light from a distant star can be approximated as a plane wavefront when it reaches Earth because the distance is so great that the curvature of the wavefronts becomes negligible.
- Similarly, a large flat surface (like a laser beam) can produce a plane wavefront.

4. **Conclusion**:
- Among the options provided, the source that produces a plane wavefront is typically a large flat surface or a distant point source (like a star).

### Final Answer:
- The answer is that a plane wavefront is produced by a plane wave source, which can be approximated by light from a distant star or a laser beam.

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