Verified Solution Science Light – Reflection and Refraction

A convex mirror is used as a security mirror in a shop. The owner observes a customer 5 m away, and her image appears to be 1/5th the actual size. Calculate the focal length of the mirror.

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Solution ✔ Verified
  • A+1.0 m
  • B+1.25 m
  • C+1.5 m
  • D+2.0 m
Explanation

Given object distance u = -5 m. Magnification m = +1/5 (virtual, erect image for convex mirror). Using m = -v/u: +1/5 = -v/(-5) = v/5. So, v = +1 m. Using mirror formula 1/f = 1/v + 1/u: 1/f = 1/1 + 1/(-5) = 1 - 1/5 = 4/5. So, f = 5/4 = +1.25 m. The positive sign indicates a convex mirror.

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