Question

optics class 12 Questions and Answers pdf 11. A convex lens and a concave lens, each having the same focal length of 25 cm, are put in contact to form a combination of lenses. The power of the combination (in dioptres) is
(a) zero
(b) 25
(c) 50
(d) infinity

Answer 1

Answer:

Power of the combination = 0 D.

Explanation:

f1 = 25 cm (Convex lens)

f2 = - 25 cm (Concave lens)

Focal length of lenses in combination :$\frac{1}{f} =\frac{1}{f1} +\frac{1}{f2}$

1/f = 1/25 - 1/25

    = 0/25 = 0

Power = 1 / focal length

P = 1 /f

  = 0 D