alleryThe focal length of a plane mirror is:
AInfinity
BZero
CEqual to its width
DEqual to the object distance
Answer & Solution
Correct answer: A. Infinity
1. A plane mirror can be viewed as a sphere of infinite radius.
2. Since f = R/2, an infinite radius gives an infinite focal length.
3. This is consistent with the fact that the image is as far behind as the object is in front.
_Source: syllabus Science, Ch 9 "Light Reflection and Refraction", §9.2_
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