Question

The width of the central maximum of a diffraction pattern on a single slit does not depend upon

• A. frequency of light used
• B. width of the slit
• C. distance between slit and source
• D. wavelength of light used

Hint:

Be careful not to mix up the two distances in a diffraction setup! The distance $D$ that alters the pattern is the distance from the slit to the screen. The distance from the source to the slit is irrelevant because optical elements (like collimating lenses) are used to make the incoming light rays parallel before they reach the slit.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
Identify which distance in a single-slit diffraction setup influences the fringe pattern and which does not.

Step 2: Key Formula or Approach:
Fringe width depends on the slit-to-screen distance D. The source-to-slit distance is rendered irrelevant by collimating optics that ensure parallel rays arrive at the slit.

Step 3: Detailed Explanation:
Optical setups typically place a collimating lens between the source and the slit to produce plane wavefronts. Consequently, shifting the source closer or farther from the slit—before the collimator—has no effect on the diffraction pattern. Only changes in the slit-to-screen separation alter the geometric spread of the fringes. Distinguishing these two distances prevents unnecessary recalculations.

Step 4: Final Answer:
Only the slit-to-screen distance affects the pattern; source-to-slit distance is irrelevant.