Three people have trouble with their eyes…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Three people have trouble with their eyes. Say which defect each has, and which lens corrects it.
- Arjun watches the television across the room easily, but a menu at arm's length is a blur.
- Leela reads her phone easily, but cannot read a bus number until the bus is close.
- Mr. Bose is years old. He needs one kind of lens to drive and another to read.
Need a reminder? The key ideaShow
Short sight (myopia): far objects blur; a concave lens with . Long sight (hypermetropia): near objects blur; a convex lens that makes a page at appear at , from . Power with in metres. Old age (presbyopia) may need bifocals.
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) Arjun sees far but not near: hypermetropia, corrected by a convex lens.
Step 2. (b) Leela sees near but not far: myopia, corrected by a concave lens.
Step 3. (c) Mr. Bose has presbyopia with age. A bifocal lens helps: concave at the top for driving, convex at the bottom for reading.
Answer: (a) hypermetropia, convex. (b) myopia, concave. (c) presbyopia, bifocal.
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