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:

In diffraction experiments, the angular width of the fringes is inversely proportional to the wavelength. A shorter wavelength results in narrower fringes.

Answer 1

The Correct Option is B

Step 1: Diffraction Pattern Basics In single-slit diffraction, light passing through a narrow slit spreads, creating a pattern. The central maximum's angular width is: \[\n\theta = \frac{\lambda}{a}\n\] Where: - \( \lambda \) is the light's wavelength. - \( a \) is the slit's width. - \( \theta \) is the central maximum's angle. Step 2: Wavelength's Impact - The diffraction pattern changes with the light's wavelength \( \lambda \). Longer wavelengths widen the central maximum (larger \( \theta \)), shorter wavelengths narrow it (smaller \( \theta \)). - Red light has a longer wavelength than blue. Replacing red with blue decreases \( \lambda \). - Consequently, the central maximum's angular width shrinks, and fringes become narrower and closer. Step 3: Summary The conclusion: fringes become narrower and more tightly packed when red light is switched for blue light. The correct answer is: \[\n\boxed{(B)} \, \text{Fringes will become narrower and crowded together.}\n\]