The fringes produced on a screen by blue monochromatic light falling upon a double-slit arrangement were found to be too close together for measurements to be taken on them. The fringe separation could be increased by

Options

A. Increasing the distance between the slits and the screen
B. Replacing the light with monochromatic red light
C. Increasing the separation of the slits
D. Decreasing the wavelength of the incident light

Answer

To solve the problem of increasing the fringe separation in a double-slit experiment where the fringes produced by blue monochromatic light are too close together, we can follow these steps:

### Step 1: Understand the formula for fringe separation
The fringe separation (Δy) in a double-slit experiment is given by the formula:
\[ \Delta y = \frac{\lambda L}{d} \]
where:
- \( \Delta y \) = fringe separation
- \( \lambda \) = wavelength of the light used
- \( L \) = distance from the slits to the screen
- \( d \) = distance between the slits

### Step 2: Identify factors affecting fringe separation
From the formula, we can see that the fringe separation is directly proportional to the wavelength (λ) and the distance to the screen (L), and inversely proportional to the slit separation (d).

### Step 3: Increase the wavelength
One way to increase the fringe separation is to use light with a longer wavelength. Since blue light has a shorter wavelength compared to red light, replacing blue light with red light (which has a longer wavelength) will increase the fringe separation.

### Step 4: Increase the distance to the screen
Another method to increase the fringe separation is to increase the distance (L) from the slits to the screen. By moving the screen further away, the fringe separation will also increase.

### Step 5: Conclusion
Thus, to increase the fringe separation, we can either:
1. Replace the blue monochromatic light with red light.
2. Increase the distance between the slits and the screen.

### Answer
The fringe separation could be increased by:
1. Replacing blue light with red light.
2. Increasing the distance between the slits and the screen.