Question

If two lenses with focal lengths 10 cm and 20 cm respectively are kept in contact with each other the effective power of combination is

Answer 1

The effective power of combination is 30 cm.

Explanation:

Given that,

Focal length of lens 1, $f_1=10\ cm$

Focal length of lens 2, $f_1=20\ cm$

The power of lens 1 will be :

$P_1=\dfrac{1}{f_1}=\dfrac{1}{10}=0.1\ m$

The power of lens 2 will be :

$P_2=\dfrac{1}{f_2}=\dfrac{1}{20}=0.2\ m$

The effective power of the combination is simply sum of powers of individual powers as :

$P=P_1+P_2$

$P=0.1+0.2$

P = 0.3 m

or

P = 30 cm

So, the effective power of combination is 30 cm. Hence, this is the required solution.

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Answer 2

Explanation:

power = 30cm or power = 0.3 cm