Past exam of the physics course of the year 1 of the natural sciences course of the University of Cambridge / 2010 / Paper 1 / Section A / 2 / Solution

For prism sweep under different rotation conventions, let the apex angle be $A=60^{\circ }$. Snell's law at both faces givesHere $e$ is measured from the second face's outward normal, whereas $D$ is the deviation from the incident direction. The two settings giveFor a fixed laser and rotating prism, the outgoing beam therefore sweepsIf instead the prism stays fixed and the input beam is steered, its exit-face normal stays fixed and the answer is $|\Delta e|=8.3325^{\circ }$. The source does not explicitly say which component moves, so the laboratory-angle convention matters. Both settings transmit through the second face; total internal reflection does not occur.