In Young.s double slit experiment sodium light is replaced by blue lamp, then the fringe width

Options

A. increase
B. decreases
C. remains same
D. becomes zero

Answer

To solve the problem regarding the change in fringe width when sodium light is replaced by a blue lamp in Young's double slit experiment, we can follow these steps:

### Step-by-Step Solution:

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

2. **Identify the Wavelengths**:
- Sodium light (which is yellow) has a longer wavelength compared to blue light. The typical wavelength of sodium light is approximately \( 589 \, \text{nm} \) (nanometers), while blue light has a shorter wavelength, typically around \( 450 \, \text{nm} \).

3. **Analyze the Effect of Changing Wavelength**:
Since the fringe width is directly proportional to the wavelength (\( \lambda \)), if the wavelength decreases (as it does when switching from sodium light to blue light), the fringe width will also decrease.

4. **Conclusion**:
Therefore, when sodium light is replaced by a blue lamp, the fringe width decreases.

### Final Answer:
The fringe width will decrease when sodium light is replaced by a blue lamp in Young's double slit experiment.