Video lecture for PHYS 130 at the University of Alberta. Here we discuss what a diffraction grating is and how it works to separate a spectrum of light into all its component frequencies. We then show what happens when light from different sources passes through a grating which in the 19th century lead to the mysterious discovery that each element emitted only certain fixed frequencies of light. [Note: this video is largely the same as the similarly titled PHYS 146 video with just a minor change to remove complex exponentials from the explanation.]

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