Question

A lens has power 4D.Find the focal length of the lens

Answer 1

power =100/focal length(in cm)
4D=100/ focal length (in cm)
focal leghth (in cm)=100÷4=25 cm


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Answer 2

Answer:

The focal length of the lens is 25 cm.

Explanation:

Given that,

Power of the lens P = 4 D

We know that,

The power of the lens is reciprocal of the focal length of the lens.

$P =\dfrac{1}{f}$.....(I)

Here, P = Power of the lens

f= focal length of the lens

Now, put the value of P in equation (I)

$4=\dfrac{100}{f}$

$f = \dfrac{100}{4}$

$f = 25\ cm$

Hence, The focal length of the lens is 25 cm.