alleryStart learning →A concave mirror has a radius of curvature of 50.0 cm. What is its focal length?
A100 cm
B50.0 cm
C-25.0 cm
D25.0 cm
Answer & Solution
Correct answer: D. 25.0 cm
1. For a spherical mirror the focal length is f = R divided by 2.
2. Substituting with units, f = 50.0 cm divided by 2 = 25.0 cm.
3. The mirror is concave, so it is a converging mirror and the focal length is positive.
4. Answering 100 cm doubles the radius instead of halving it, and answering -25.0 cm would describe a convex mirror.
_Source: OpenStax College Physics (CC BY 4.0), Ch 25 "Geometric Optics", section 25.7 Image Formation by Mirrors_
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