Double slit interference experiment is carried out with monochromatic light and interference fringes are observed. If now monochromatic light is replaced by white light, what change is expected in interference pattern?

Options

A. NO change
B. Pattern disappears
C. White and dark fringes are observed throughout
D. A few coloured fringes are observed on either side of central white fringe

Answer

### Step-by-Step Solution:

1. **Understanding Monochromatic Light**:
- Monochromatic light consists of waves of a single wavelength (λ). In a double slit interference experiment using monochromatic light, the interference pattern produced consists of alternating dark and bright fringes due to constructive and destructive interference.

2. **Understanding White Light**:
- White light is a mixture of multiple wavelengths (colors) ranging from violet (around 400 nm) to red (around 700 nm). Each color will produce its own interference pattern due to its unique wavelength.

3. **Effect on the Central Maximum**:
- When white light is used, the central maximum will still appear white because all the colors overlap at this point. This is because the path difference for all wavelengths at the central maximum is zero, leading to constructive interference for all colors.

4. **Effect on Fringes Away from the Center**:
- As we move away from the central maximum, the path difference for different wavelengths will vary. This means that different colors will constructively interfere at different positions, leading to colored fringes. For example, violet light (shorter wavelength) will reach a maximum at a different position compared to red light (longer wavelength).

5. **Resulting Pattern**:
- The result will be a central white fringe (where all colors overlap) with colored fringes on either side. The fringes will not be as sharply defined as in the monochromatic case, and the colors will blend, creating a spectrum effect.

6. **Conclusion**:
- The expected change in the interference pattern when monochromatic light is replaced by white light is that a central white fringe will be observed, surrounded by colored fringes on either side.

### Final Answer:
A few colored fringes are observed on either side of the central white fringe.