A narrow beam of light goes through a glass slab, and then through a glass prism…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A narrow beam of light goes through a glass slab, and then through a glass prism. In which case is the emergent ray parallel to the incident ray? Explain.
Need a reminder? The key ideaShow
In a prism, and the deviation is . At each face, Snell's law: and . The deviation is least when the ray passes symmetrically, with .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The slab. Its faces are parallel. The bend going in is undone going out, so the ray leaves parallel, only shifted sideways.
Step 2. The prism. Its faces are not parallel. Both bends turn the ray toward the base, so they add up, and the ray leaves at an angle: the deviation.
Answer: the slab.
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