A convex lens has a focal length of 17 cm.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A convex lens has a focal length of .
- How far from the lens is each of its two foci?
- Where is on each side?
- A parallel beam falls on the lens. At what distance do the rays meet?
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. (a) Both foci are from the lens, one on each side.
Step 2. (b) is from the lens, on each side.
Step 3. (c) The parallel beam meets at , behind the lens.
Answer: (a) . (b) . (c) .
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