Question

A real image 4/5 size of object is formed at 18cm from a lens. Calculate the focal length of the lens.

Answer 1

The focal length of the lens is 10 cm.

Explanation:

Given that,

A real image 4/5 size of object is formed at 18 cm from a lens.

Image distance, v = +18 cm

Magnification, $m=\dfrac{h'}{h}=\dfrac{4}{5}$

So,

$\dfrac{h'}{h}=\dfrac{-4}{5}=\dfrac{v}{u}\\\\4u=-5v\\\\4u=-5\times 18\\\\u=-22.5\ cm$

Using lens formula :

$\dfrac{1}{f}=\dfrac{1}{v}-\dfrac{1}{u}\\\\\dfrac{1}{f}=\dfrac{1}{(18)}-\dfrac{1}{(-22.5)}\\\\f=10\ cm$

So, the focal length of the lens is 10 cm.

Learn more,

Lens formula

https://brainly.in/question/12414173

Answer 2

Answer:

hi this is the answer of you qns.

Explanation:

hope you will be satisfied with this.