How to say positivity or negativity belongs to a power,how can any distance be negative????
Why and How does the lens formula changes due to this??
please answer fast

Dear Student,

The power of a lens is depends upon the focal length of the lens used. The focal length of the convex lens is postive and that of a concave is negative.
$P=\frac{1}{f}$

The distance is not negative it just a sign convention that we take, which makes the distance on the left of the lens negative and to the right of the lens positive.


$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
Depending upon the sign convention v, u and f will change as the lens formula changes.

Regards