MCQ practice · SSC Physics Board questions · Chapter 8: Reflection of Light
Where is the centre of curvature of a plane mirror situated?
Think it through first, then pick an option.
- a at the principal focus
- b on the focal plane
- c at the secondary focus
- d at infinity
Answer and explanation
Correct answer: d at infinity
The radius of curvature is r = 2f and the focal length of a plane mirror is infinite, so its centre of curvature is at infinity too. A plane mirror can be thought of as a spherical mirror of infinite radius.
Why the other options are wrong
- a at the principal focus: This is not the answer: The radius of curvature is r = 2f and the focal length of a plane mirror is infinite, so its centre of curvature is at infinity too. A plane mirror can be thought of as a spherical mirror of infinite radius.
- b on the focal plane: This is not the answer: The radius of curvature is r = 2f and the focal length of a plane mirror is infinite, so its centre of curvature is at infinity too. A plane mirror can be thought of as a spherical mirror of infinite radius.
- c at the secondary focus: This is not the answer: The radius of curvature is r = 2f and the focal length of a plane mirror is infinite, so its centre of curvature is at infinity too. A plane mirror can be thought of as a spherical mirror of infinite radius.
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