For a given single-slit, the diffraction pattern is obtained on a fixed screen first by using red light and then with blue light. In which case, will the central maxima, in the observed diffraction pattern, have a larger angular width?

The central maxima will have a larger angular width with red light because red light has a longer wavelength than blue light. The angular width of the central maxima is directly proportional to the wavelength of the light used.

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