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TheJeeronian t1_jadj47s wrote

Reply to comment by breckenridgeback in ELI5 How does an optical prism work? And why? by Small_Conference_227

Not all of the sides on a cube are parallel. Specifically, any two adjacent sides.

That said, even returning the rays to parallel does not mean recombining them. At the first surface they are given different angles, splitting one beam. Returning this set of beams to parallel just means that the colors do not spread even further once they've left.

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breckenridgeback t1_jadl2xu wrote

> That said, even returning the rays to parallel does not mean recombining them. At the first surface they are given different angles, splitting one beam. Returning this set of beams to parallel just means that the colors do not spread even further once they've left.

This is true, but the effect is pretty small, much narrower than a typical light beam, and dominated by diffraction, so you just get fringes of very slight color.

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