Question

A convex lens focal length 18cm and a concave lens of focal length 24 cm are placed in contact such that they have a cimmon principal axis.Wll the combinatin act as a convex lens or a concave lens? Find the focal length and power of the combination

Answer 1

combined focal length is given as

1/f(net)=1/f1+1/f2

1/f=1/18-1/24

(for convex lens f is taken in +ve for concave lens f is taken in -ve)

1/f=24-18/432

1/f=6/432

f=432/6

f=72 cm

so resultant focal length is in +ve so the combination behaves as an convex lens

power of lens is given as reciprocal of focal length in meteres

P=1/f

P=1/(72/100) (divide it by 100 to convert into meteres)

P=100/72

P=1.38 D

hope this helps and u understand well

:))

Answer 2

Explanation:

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