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In a single-slit diffraction pattern, what happens as the slit width is increased?

1. the peak intensity of the central maximum increases and its angular width decreases
2. the peak intensity of the central maximum increases and its width also increases
3. the peak intensity of the central maximum decreases and its width increases
4. the peak intensity of the central maximum decreases and its width also decreases

Correct answer: the peak intensity of the central maximum increases and its angular width decreases

Solution

The central maximum's angular half-width is lambda/a, so increasing a narrows it. A wider slit also lets through more light energy concentrated into a smaller region, so the peak intensity rises. Hence peak intensity increases and width decreases.

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