Question

A converging lens of 4 diopter is combined with diverging lens of -2 diopters.Find the power and focal length Of The combination​

Answer 1

Answer:

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Answer 2

Answer:

Given:

Converging lens has power = 4 D is combined with Diverging lens of power = - 2D.

To find:

Power and focal length of the combination .

Concept:

For a combination of lens, the power or convergence or divergence is algebraically added taking positive/negative signs into consideration.

$\boxed{ \red{ \large{P_{combination} = P_{1} + P_{2}}}}$

We know that Power is the Reciprocal of Focal Length :

$\boxed{ \blue{ \large{= > \dfrac{1}{f_{combination}} = \dfrac{1}{f1} + \dfrac{1}{f2}}}}$

Calculation:

$\large{P_{combination} = 4 + ( - 2) }$

$\large{ = > P_{combination} =2 \: dioptre}$

Focal length of the combination :

$f = \dfrac{1}{p} = \dfrac{1}{2} = 0.5 \: m = 50 \: cm$

So the combination acts like a converging or convex lens.