Question

You are standing 4.5m from a convex security mirror in a store. You estimate the height of your image to be half of your actual height.

Estimate the radius of curvature of the mirror. Follow the sign conventions.

Answer 1

Start with the magnification

M = -q/p

Since M = .5, then .5 = -q/p, so -.5p=q

(-.5)(4.5) = q

q = -2.25

Then apply 1/f = 1/p + 1/q

1/f = 1/4.5 + 1/-2.25

f = -4.5 m

SInce R = 2f, R = 2(-4.5)

R = -9 m