Question

You are given lenses with powers +10 d,+5d,-5d,-20d and -10d taking a pair of lenses at a time which two lenses will you select to have a combination of total focal length when the two lenses are kept in contact in each case (1) 20cm (2) -10cm (3) -20vm (4) 20/3

Answer 1

Answer:

1. +5D,-10D

2.+10d,-20d

3.

Answer 2

Answer:

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