Unit of power of a lens is m 1. Focal length also determines angle of view and apparent perspective or whether a lens is wide angle normal or telephoto. A curved mirror in which mirroring surface bulges towards the light source is known as the convex mirror.
The power of a lens is specified as P 1 F where f is the focal length.
Note that the angle above A replaces this entire expression not just the a. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens. A curved mirror in which mirroring surface bulges towards the light source is known as the convex mirror. There is no formula to calculate the focal length of your telescope.