Question

The magnification of a convex mirror is +0.65X for objects 2.8 m from the mirror. What is the focal length of this mirror?

Answer 1

Since it is convex, the focal length is negative. From the magnification,you know that the image distance is Di = -0.65 Do. The image distance Di is negative because it is a virtual image, behind the mirror.

Now solve

1/Do + 1/Di = 1/Do -1/0.65 Do = 1/f
(1 - 1.538)/Do = 1/f

-0.538/Do = 1/f

f = -1.86 Do = -5.2 m

Answer 2

Thank you!