A student sets up an experiment to investigate double-slit interference. The student uses light of a single wavelength from a laser to illuminate a double slit so that a pattern of interference fringes is observed on the screen. [Figure showing a double-slit experiment setup with laser, double slit, screen, and distances p, r, q] The student finds that the fringes are very close together. What could the student decrease in order to increase the separation of the fringes on the screen?

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