Question

when two lenses are placed coaxially in contact with each other the effective focal length of the combination is given by the relation.........​

Answer 1

Explanation:

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Answer 2

Given:

Two lenses are placed coaxially in contact with each other.

To find:

Relation giving the equivalent focal length of the combination ?

Calculation:

When the lens are placed coaxially , the net power (net converging/diverging capability) is given by algebraic addition of power of individual lens.

• Let the individual powers be P1 and P2.

• Let the individual focal lengths be f1 and f2.

$\sf\therefore \: P = P_{1} + P_{2}$

$\sf\implies \: P = \dfrac{1}{f_{1}} + \dfrac{1}{f_{2}}$

$\sf\implies \: \dfrac{1}{f} = \dfrac{1}{f_{1}} + \dfrac{1}{f_{2}}$

So, the required relationship is :

$\boxed{ \bold{ \: \dfrac{1}{f} = \dfrac{1}{f_{1}} + \dfrac{1}{f_{2}}}}$