Question

the power of convex lens in 5 dioptre. its focal length is ?

Answer 1

Here is your answer

Power of lens=1/f=2.5D

f=focal length in metre

2.5=1/f

Hence

f=1/2.5

f=0.4m

Hence focal length is 0.4metre (40cm)

Answer 2

Answer:

The focal length of the lens is 20 cm.

Explanation:

Given that,

Power of the lens P = +5 D

We know that,

The power of convex lens is positive.

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)

$5=\dfrac{100}{f}$

$f = \dfrac{100}{5}$

$f = 20\ cm$

Hence, The focal length of the lens is 20 cm.