Young's double slit experiment is performed with monochromatic light. A thin film is introduced in front of one of the slits

Options

A. Intensity at the position of central maxima must decrease
B. Intensity at the position of central maxima may increase
C. Central maxima may remain unshifted
D. Intensity at position of first maxima may decreases

Answer

### Step-by-Step Solution:

1. **Understanding Young's Double Slit Experiment**:
- In Young's double slit experiment, light from a monochromatic source passes through two closely spaced slits (S1 and S2) and creates an interference pattern on a screen. The central maximum occurs at the point where the path difference between the light waves from the two slits is zero.

2. **Introducing a Thin Film**:
- When a thin film is introduced in front of one of the slits (let's say in front of slit S1), it alters the effective path length of the light coming from that slit. The film introduces a phase change due to its thickness and refractive index.

3. **Effect on Intensity**:
- The introduction of a thin film will generally reduce the intensity of light coming from the slit in front of the film. This is because some light is reflected at the air-film interface and some is absorbed by the film.

4. **Central Maximum**:
- The central maximum remains at the same position because the path difference at the center is still zero. However, the overall intensity at the central maximum may not change significantly, as it depends on the combined intensity from both slits.

5. **First Maximum**:
- The position of the first maximum will shift due to the change in effective path length caused by the thin film. Since the intensity of light from one slit has decreased, the intensity at the position of the first maximum will also decrease.

6. **Conclusion**:
- Therefore, while the central maximum remains unshifted, the intensity at the position of the first maximum decreases. Hence, the correct answer to the question is that the intensity at the position of the first maxima may decrease.

### Final Answer:
The intensity at the position of the first maxima may decrease.

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