4 a thin lens has a focal length of 25 cm what is the power of the lens and what is its nature

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A thin lens has a focal length 25 cm. Calculate the power of lens in dioptre.

Solution

The correct option is A -4Given: The focal length of a lens is

$f=-25cm=\frac{-25}{100}m=-0.25m$

The power of the lens is given by

$P=\frac{1}{f\text{(in metre)}}$

$P=\frac{1}{-0.25m}$
$P=-4D$