Question

Find the net focal length of a combination of lenses whose focal length are

Answer 1

Net focal length = f

Individual focal lengths be

$f_{1} \: \: f_{2} \: \: f_{3} \: .........\: f_{n}$

Then,

$\frac{1}{f} = \frac{1}{f_{1}} + \frac{1}{f_{2}} + \frac{1}{f_{3}} + ...... + \frac{1}{f_{n}}$

Hope this helps!

Answer 2

Answer:

The joining point of light ray to the principles axis after reflection when it comes parallel to principle axis to fall on mirror surface is known as focus