Question

A mirrored-glass gazing globe in a garden is 28.0 cm in diameter. part a what is the focal length of the glob

Answer 1

For a curved mirror, the radius of curvature R is twice the focal length f:
$R=2f$ (1)
Since the diameter d is twice the radius R, we can rewrite (1) as
$\frac{d}{2} = 2f$
From which we can calculate the focal length from the diameter:
$f= \frac{d}{4}= \frac{28.0 cm}{4}=7.0 cm$