Question

The diffraction fringes obtained by a single slit are of

• A. equal width
• B. equal width and unequal intensity
• C. unequal width but equal intensity
• D. unequal width and unequal intensity

Hint:

Physics Tip: Unlike Young's Double Slit Experiment (where interference fringes are roughly equal in width and intensity), a single-slit diffraction pattern is dominated by a very broad and bright central peak.

Answer 1

The Correct Option is D

Concept: Physics (Optics) - Single-Slit Diffraction.

Step 1: Analyze the intensity distribution. In single-slit diffraction, the central maximum is the brightest. As the order of the fringes ($m$) increases, the intensity of the subsequent maxima decreases significantly. Therefore, the fringes are of unequal intensity.

Step 2: Analyze the fringe width. The position of the minima is given by $d \sin \theta = m\lambda$. The central maximum is twice as wide as the secondary maxima. Furthermore, because the sine function is non-linear, the angular separation between higher-order minima changes. Therefore, the fringes are of unequal width.

Step 3: Conclusion. Both the width and the intensity of the fringes vary across the diffraction pattern. The central maximum is the widest and brightest, with fringes becoming narrower and dimmer moving away from the center. $$ \therefore \text{The fringes have unequal width and unequal intensity.} \text{ } $$