Question

If the separation between the two slits in Double Slit Fraunhofer Diffraction is changed, what change will be observed in the diffraction pattern?

• A. The fringe length will increase
• B. The fringe length will decrease
• C. Fringes will be colored
• D. No change

Hint:

In a double-slit diffraction pattern, the fringe separation is inversely proportional to the slit separation.

Answer 1

The Correct Option is B

Step 1: Understanding Double Slit Fraunhofer Diffraction
In the double-slit diffraction pattern, the fringe separation \( \Delta y \) is given by the formula: \[ \Delta y = \frac{\lambda D}{d} \] Where:
\( \lambda \) is the wavelength of light,
\( D \) is the distance from the slits to the screen,
\( d \) is the separation between the slits.

Step 2: Effect of Changing the Slit Separation
If the slit separation \( d \) is increased, the fringe separation \( \Delta y \) will decrease, meaning the fringes will become closer together.
Conversely, if the slit separation decreases, the fringes will spread out.
Step 3: Conclusion Thus, when the separation between the slits is changed (increased), the fringe length will decrease.