For the sustained interference of light, the necessary condition is that the two sources should

Options

A. have constant phase difference
B. be narrow
C. be close to each other
D. of same amplitude

Explanation

To solve the question regarding the necessary condition for sustained interference of light, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding Interference**: Interference of light occurs when two or more light waves overlap and combine to form a new wave pattern. This phenomenon is crucial in various applications, including optics and telecommunications.

2. **Identifying Coherent Sources**: For sustained interference to occur, the light sources must be coherent. Coherent sources are those that maintain a constant phase relationship over time. This means that the waves emitted from these sources have a fixed phase difference.

3. **Phase Difference**: The phase difference (φ) between the two waves is a critical factor in determining the nature of the interference. If the phase difference remains constant, the interference pattern will be stable and observable.

4. **Condition for Sustained Interference**: The necessary condition for sustained interference is that the two sources should have a constant phase difference. This means that the phase difference does not vary with time, ensuring that the interference pattern remains consistent.

5. **Conclusion**: Therefore, the answer to the question is that for sustained interference of light, the two sources must be coherent, meaning they have a constant phase difference that does not change over time.

### Final Answer:
For the sustained interference of light, the necessary condition is that the two sources should be coherent.