Two thin lenses of focal length 20 cm and 25 cm are in contact. The effective power of the combination is

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Question: Answered & Verified by Expert

Two thin lenses of focal length

20 cm

and

25 cm

are in contact. The effective power of the combination is

PhysicsRay OpticsNEET

Options:

A $4.5 D$
B $18 D$
C $45 D$
D $9 D$

Solution:

1434 Upvotes Verified Answer

The correct answer is:

9 D

According to the question

P_{1} = \frac{100}{20} = 5 D, P_{2} = \frac{100}{25} = 4 D

Effective power

P = P_{1} + P_{2}

= 5 + 4 = 9 D

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