A parallel beam of light falls on three pieces of glass…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A parallel beam of light falls on three pieces of glass. After X the beam meets at a point. After Y it spreads out. After Z it stays parallel. Say what kind of lens X and Y are, and what Z could be.
Need a reminder? The key ideaShow
A convex lens is thick in the middle and brings parallel rays together at . A concave lens is thin in the middle and spreads them, as if from . A lens has a focus on each side, from the optical centre ; is away. A ray through goes straight on.
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. X. The beam meets at a point: a convex lens.
Step 2. Y. The beam spreads: a concave lens.
Step 3. Z. Nothing changes: a flat sheet of glass with parallel faces, or a lens of very long focal length.
Answer: X convex, Y concave, Z hardly bends light at all.
Check. A convex lens is thick in the middle; a concave lens is thin in the middle.
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