Question

the magnifying power of magnifying glass is 3,then focal length will be?

Answer 1

25/3.....,.........
....

Answer 2

The focal length is $12.5cm$

Given-magnifying power of magnifying glass is $3$

Find the focal length

The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative focal length indicates that the system diverges light

If the image is formed at least distance of distinct vision. Then, magnify power is given, $m=1+\frac{D}{f}$

where D is the least distance of distinct vision$=25cm$

f is the focal length

m is the magnifying power

putting in values in formula of m,

we get,

$m=1+\frac{D}{f}$

$\Rightarrow 3=1+1\frac{25}{f}$

$\Rightarrow 2=\frac{25}{f}$

$\Rightarrow f=\frac{25}{2} =12.5cm$

Hence, the focal length is $12.5cm$

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