Question

Roovi is given lenses with powers +5d , -5d , +10d , -10d and -20d considering a pair of lenses at a time which two lenses will be select to have a combination of focal length when two lenses are kept in contact in each case?

Answer 1

You are given lenses with powers + 10D,+ 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.

(i) 20 cm (ii) - 10 cm (iii) - 20 cm (iv) 20/3 cm