A compound lens is made up of two thin lenses having power $ +12.5 \mathrm{D} $ and $ -2.5 \mathrm{D} $ . Find the focal length and power of the combination.

Given:
$\mathrm{P}_{1}=12.5 \mathrm{D}$
$\mathrm{P}_{2}=-2.5 \mathrm{D}$
To find: focal length and power of the combination

Solution:

Equivalent power; $\mathrm{P}=\mathrm{P}_{1}+\mathrm{P}_{2}=12.5-2.5=10 \mathrm{D}$

focal length equivalent $=\frac{1}{10} \mathrm{~m}=10 \mathrm{~cm}$
 

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Updated on: 10-Oct-2022

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