In Young's double-slit experiment, if yellow light is replaced by blue light, the interference fringes become

Options

A. Darker
B. Brighter
C. Wider
D. Narrower

Answer

To solve the problem regarding the effect of replacing yellow light with blue light in Young's double-slit experiment, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Fringe Width**:
In Young's double-slit experiment, the fringe width (β) is given by the formula:
\[ \beta = \frac{\lambda D}{d} \]
where:
- \( \beta \) = fringe width
- \( \lambda \) = wavelength of light used
- \( D \) = distance from the slits to the screen
- \( d \) = distance between the slits

2. **Identify the Wavelengths**:
- The wavelength of yellow light is greater than that of blue light. For example, yellow light has a wavelength around 580 nm, while blue light has a wavelength around 450 nm.

3. **Analyze the Effect of Wavelength on Fringe Width**:
- Since fringe width (β) is directly proportional to the wavelength (λ), if the wavelength decreases (as it does when switching from yellow to blue light), the fringe width will also decrease.

4. **Conclusion**:
- Therefore, when yellow light is replaced by blue light, the fringe width becomes narrower.

5. **Final Answer**:
- The interference fringes become narrower.