Question

A combination of lens contains two converging lens of focal length 30 cm
and 50 cm and a diverging lens of focal length 40 cm. Find the power and
focal length of the combination.

Answer 1

hope this helps you

Answer 2

Given that,

Focal length of first converging lens or convex lens, $f_1=+30\ cm$

Focal length of second converging lens or convex lens, $f_2=+50\ cm$

The focal length of diverging lens, $f_3=-40\ cm$

To find,

The power and  focal length of the combination.

Solution,

The power of the combination of lenses is given by :

$P=P_1+P_2+P_3\\\\P=\dfrac{1}{f_1}+\dfrac{1}{f_2}+\dfrac{1}{f_2}\\\\P=\dfrac{1}{30}+\dfrac{1}{50}+\dfrac{1}{(-40)}\\\\P=0.0283\ m^{-1}\\\\P=2.83\ D$

The reciprocal of power is equal to the focal length of the lens. So,

$f=\dfrac{1}{P}\\\\f=\dfrac{1}{2.83}\\\\f=0.353\ m\\\\f=35.3\ cm$

Hence, this is the required solution.

Learn more,

Combination of lens

https://brainly.in/question/7766174