Question

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

• A. the diffraction pattern will disappear.
• B. fringes will become narrower and crowded together.
• C. fringes will become broader and will be further apart.
• D. there is no change in the diffraction pattern.

Hint:

Diffraction width: \begin{itemize} \item Larger wavelength ⇒ wider fringes. \item Smaller wavelength ⇒ narrow fringes. \end{itemize}

Answer 1

The Correct Option is B

Concept: In single slit diffraction: \[ \text{Fringe width} \propto \lambda \] Step 1: Compare wavelengths. \[ \lambda_{\text{blue}} < \lambda_{\text{red}} \] Step 2: Effect on pattern. Smaller wavelength ⇒ smaller fringe width. Step 3: Conclusion. Fringes become narrower and closer together.