Question

How to find out the focal length of a concave mirror Quickly but approximately ?

Answer 1

to find the focal length of a concave mirror you can do the following steps which I am telling to you

firstly remember the formula of finding the focal length

$f = \frac{r}{2}$

where f is the focal length and R is the radius of curvature

so you can quickly find the focal length by simply dividing the the radius of curvature of the concave mirror by 2