A convex lens of power +6 D is placed in contact with a concave lens of power -2.5 D.
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 of power is placed in contact with a concave lens of power . Find the power and the focal length of the pair. Does the pair act as a convex or a concave lens?
Need a reminder? The key ideaShow
Power with in metres, in dioptres (D). Convex lenses have a positive power, concave lenses a negative power. For thin lenses in contact, the powers add: .
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 power. .
Step 2. The focal length. .
Answer: and ; the pair acts as a convex lens.
Check. The convex lens is the stronger one, so the pair converges, but less than the convex lens alone.
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