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 will analyze the relationship between the wavelength of light and the spacing of the interference fringes.

### Step-by-Step Solution:

1. **Understanding the Concept of Interference Fringes**:
- In Young's double-slit experiment, light passing through two slits creates an interference pattern of bright and dark fringes on a screen. The position and spacing of these fringes depend on the wavelength of the light used.

2. **Identifying Wavelengths of Yellow and Blue Light**:
- Yellow light has a longer wavelength compared to blue light. For example, the wavelength of yellow light is approximately 580 nm, while the wavelength of blue light is around 450 nm.

3. **Formula for Fringe Spacing**:
- The fringe spacing (β) in Young's double-slit experiment is given by the formula:
\[ \beta = \frac{\lambda D}{d} \]
where:
- \( \beta \) = fringe spacing
- \( \lambda \) = wavelength of light
- \( D \) = distance from the slits to the screen
- \( d \) = distance between the slits

4. **Effect of Changing Wavelength**:
- From the formula, we can see that fringe spacing (β) is directly proportional to the wavelength (λ). This means that if the wavelength decreases, the fringe spacing will also decrease.

5. **Replacing Yellow Light with Blue Light**:
- Since blue light has a shorter wavelength than yellow light, replacing yellow light with blue light will decrease the value of λ in the formula. Consequently, the fringe spacing β will also decrease.

6. **Conclusion**:
- Therefore, when yellow light is replaced by blue light in Young's double-slit experiment, the interference fringes will become closer together.

### Final Answer:
The interference fringes become closer together when yellow light is replaced by blue light.