An interference pattern is formed on the screen, when light from two different monochromatic sources are allowed to interfere. Then, it is true that

Options

A. Frequencies of light from the two sources are equal to each other
B. The sources are coherent
C. The sources should be located in the same medium
D. The path difference should either be an even or an odd multiple of `lambda // 2`, where `lambda` is the wavelength of light

Answer

To solve the question regarding the interference pattern formed by two different monochromatic light sources, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Coherence**:
- For an interference pattern to be formed, the two light sources must be coherent. This means that they should maintain a constant phase relationship over time.

**Hint**: Recall that coherence is essential for producing stable interference patterns.

2. **Frequency of Light Sources**:
- Since the sources are monochromatic and coherent, the frequencies of the light from both sources must be equal. If the frequencies were different, the phase relationship would not remain constant, and no stable interference pattern would form.

**Hint**: Think about how frequency relates to wavelength and phase in wave phenomena.

3. **Location of Sources**:
- The two sources must be located in the same medium. This ensures that the speed of light in both paths is the same, which is crucial for maintaining a constant phase difference.

**Hint**: Consider how the medium affects the speed of light and, consequently, the interference pattern.

4. **Path Difference**:
- The path difference between the two sources must be such that it results in constructive or destructive interference. However, it does not need to be an even multiple of λ/2 for an interference pattern to exist; it can be any integer multiple of the wavelength λ for constructive interference.

**Hint**: Remember that constructive interference occurs when the path difference is a multiple of the wavelength.

5. **Conclusion**:
- Based on the above points, we conclude that the correct statements about the interference pattern formed by two different monochromatic sources are:
- The frequencies of light from the two sources are equal.
- The sources must be in the same medium.

**Hint**: Summarize the conditions for interference and check which options align with these conditions.

### Final Answer:
The true statements regarding the interference pattern formed by two different monochromatic sources are:
- The frequencies of light from the two sources are equal.
- The sources should be located in the same medium.