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A concave mirror has a focal length of 15 cm. Using R equals twice f, what is its radius of curvature?
A7.5 cm
B22.5 cm
C30 cm
D225 cm
Answer & Solution
Correct answer: C. 30 cm
1. The radius of curvature equation is R = 2f.
2. Substituting f = 15 cm gives R = 2 x 15 cm.
3. Carrying out the multiplication gives R = 30 cm.
4. 7.5 cm comes from dividing by two instead of multiplying, and 225 cm comes from squaring f instead of doubling it.
_Source: OpenStax Physics (CC BY 4.0), Ch 16 "Mirrors and Lenses", section 16.1 Reflection_
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