If a torch is used in place of monochromatic light in Young's experiment what will happen?

Options

A. Fringe will appear for a moment then it will disappar
B. Fringes will appear as for monochrcmatic light
C. Only bright fringes will appear
D. No fringes will appear

Answer

### Step-by-Step Solution:

1. **Understanding Young's Experiment**:
- Young's double-slit experiment is designed to demonstrate the wave nature of light through interference patterns created by coherent light sources passing through two closely spaced slits.

2. **Monochromatic Light Source**:
- In the original experiment, a monochromatic light source (like a laser) is used, which emits light of a single wavelength (λ). This results in clear interference patterns consisting of alternating bright and dark fringes on the screen due to constructive and destructive interference.

3. **Replacing with Torch Light**:
- When a torch is used instead of a monochromatic light source, the light emitted from the torch consists of multiple wavelengths (colors). This means that the light is not coherent, as it contains a spectrum of wavelengths.

4. **Effect on Interference Pattern**:
- Since the torch light has different wavelengths, each wavelength will produce its own interference pattern. However, these patterns will not align perfectly due to the different wavelengths. As a result, the bright and dark fringes from different wavelengths will overlap.

5. **Resulting Observation**:
- The overlapping of multiple interference patterns will lead to a situation where the distinct bright and dark fringes are no longer observable. Instead, the screen will appear uniformly bright, as the fringes will effectively wash out due to the lack of coherence.

6. **Conclusion**:
- Therefore, when a torch is used in place of monochromatic light in Young's experiment, no distinct interference fringes will be observed. The screen will appear bright without any clear pattern.

### Final Answer:
No distinct interference fringes will appear when a torch is used in place of monochromatic light in Young's experiment.

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