A single slit diffraction pattern is obtained using a beam of red light. If the red light is replaced by the blue light, then the diffraction pattern

Options

A. remains unchanged
B. becomes narrower
C. becomes broader
D. will disappear

Answer

To solve the problem regarding the change in the diffraction pattern when red light is replaced by blue light in a single slit diffraction setup, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Single Slit Diffraction**:
- A single slit diffraction pattern is created when light passes through a narrow slit and spreads out, forming a pattern of bright and dark fringes on a screen. The central maximum is the brightest part, followed by alternating dark and bright fringes.

2. **Identifying the Wavelengths**:
- Red light has a longer wavelength (approximately 620-750 nm) compared to blue light (approximately 450-495 nm). Thus, when red light is replaced by blue light, the wavelength (λ) decreases.

3. **Fringe Width Formula**:
- 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

4. **Effect of Wavelength on Fringe Width**:
- Since fringe width is directly proportional to the wavelength (λ), a decrease in wavelength (from red to blue light) will result in a decrease in fringe width (β).

5. **Conclusion on the Diffraction Pattern**:
- As the wavelength decreases when switching from red light to blue light, the fringe width becomes narrower. This means that the diffraction pattern will have closer spaced fringes compared to the pattern produced by red light.

### Final Answer:
When red light is replaced by blue light in a single slit diffraction experiment, the diffraction pattern becomes narrower due to the decrease in wavelength.