A diffraction pattern is obtained using a beam of redlight. What happens if the red light is replaced by blue light

Options

A. No change.
B. Diffraction bands become narrower and crowded together.
C. Band become broader and farther apart.
D. Bands disappear altogether.

Explanation

To solve the question regarding the effect of replacing red light with blue light in a diffraction pattern, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Diffraction**:
- Diffraction is the bending of waves around obstacles and the spreading of waves when they pass through small openings. The pattern observed is influenced by the wavelength of the light used.

2. **Wavelength of Light**:
- Red light has a longer wavelength (approximately 620-750 nm) compared to blue light (approximately 450-495 nm).

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

4. **Effect of Wavelength on Fringe Width**:
- From the formula, we can see that fringe width (β) is directly proportional to the wavelength (λ). This means that if the wavelength increases, the fringe width increases, and if the wavelength decreases, the fringe width decreases.

5. **Comparing Red and Blue Light**:
- Since red light has a longer wavelength than blue light, substituting red light with blue light will result in a decrease in the fringe width.
- Therefore, the fringe width for blue light (β_blue) will be less than that for red light (β_red):
\[ \beta_{red} > \beta_{blue} \]

6. **Conclusion**:
- When red light is replaced by blue light, the diffraction pattern will become narrower due to the shorter wavelength of blue light.

### Final Answer:
When red light is replaced by blue light, the diffraction pattern becomes narrower.