alleryStart learning →A makeup mirror has a power of 1.50 D. What is its focal length?
A1.50 m
B0.667 m
C0.150 m
D6.67 m
Answer & Solution
Correct answer: B. 0.667 m
1. Just as for lenses, power and focal length are linked by P = 1 divided by f for a mirror.
2. Rearranging gives f = 1 divided by P.
3. Substituting with units, f = 1 divided by 1.50 D = 0.667 m.
4. The positive value is consistent with a concave converging mirror, which is what a makeup mirror uses.
5. Answering 0.150 m slips a factor of ten and would describe a far more powerful mirror than 1.50 D.
_Source: OpenStax College Physics (CC BY 4.0), Ch 25 "Geometric Optics", section 25.7 Image Formation by Mirrors_
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