Question

If two lenses with focal lengths 10cm and 20 cm respectively are kept in contact with each other, the
effective power of the combination is_______.
(1) 10 D
(2) 15 D
(3) 30 D
(4) 35 D​

Answer 1

Answer:

15 D.

Explanation:

If two lenses with focal lengths 10 cm and 20 cm respectively are kept in contact with each other, the effective power of the combination is 15 D.

Answer 2

Answer:

The correct answer is (2) 15 D