In the phenomenon of diffraction of light, when blue light is used in the experiment instead of red light , then

Options

A. Fringes will become narrower
B. Fringes will become broader
C. No change in fringe width
D. Fring will disappear

Answer

To solve the question regarding the effect of using blue light instead of red light in the diffraction of light, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Diffraction**:
- Diffraction is the bending of light waves around obstacles and the spreading out of waves when they pass through a narrow opening (like a slit).
- The diffraction pattern consists of bright and dark fringes on a screen placed at a distance from the slit.

2. **Identify the Formula for Fringe Width**:
- The fringe width (β) in a single-slit diffraction pattern is given by the formula:
\[ \beta = \frac{\lambda D}{d} \]
where:
- \( \beta \) = fringe width
- \( \lambda \) = wavelength of light
- \( D \) = distance from the slit to the screen
- \( d \) = width of the slit

3. **Analyze the Change in Wavelength**:
- When blue light is used instead of red light, the wavelength of blue light (\( \lambda_b \)) is shorter than that of red light (\( \lambda_r \)).
- Typical values are approximately:
- Red light: \( \lambda_r \approx 700 \, nm \)
- Blue light: \( \lambda_b \approx 450 \, nm \)

4. **Determine the Effect on Fringe Width**:
- Since fringe width is directly proportional to the wavelength (\( \beta \propto \lambda \)), if the wavelength decreases (as it does when switching from red to blue light), the fringe width will also decrease.
- Therefore, when blue light is used, the fringe width will become narrower.

5. **Conclusion**:
- The correct answer to the question is that the fringes will become narrower when blue light is used instead of red light.

### Final Answer:
- The fringes will become narrower (Option 1).