A convex mirror has a radius of curvature of 3.00 cm. What are its focal length and its power?

1. The focal length of a spherical mirror is half the radius of curvature, so its size is 3.00 cm divided by 2 = 1.50 cm. 2. The focal length and power of a convex mirror are negative, since a convex mirror is a diverging mirror. 3. So f = -1.50 cm. 4. Power is P = 1 divided by f with f in metres, so convert: -1.50 cm = -0.0150 m. 5. Substituting, P = 1 divided by (-0.0150 m) = -66.7 D. 6. Both answers carry the minus sign, which is the signal that this mirror spreads the rays it reflects. 7. The -1.50 D option copies the focal length figure into the power, skipping both the reciprocal and the unit conversion. _Source: OpenStax College Physics (CC BY 4.0), Ch 25 "Geometric Optics", section 25.7 Image Formation by Mirrors_