The Problem:
A small object lies 4 cm to the left of the vertex of a concave mirror who radius of curvature is 12 cm. Find the magnification of the image. Include a basic sketch to show the relation of the image to the object position relative to the mirror.
Solution:
We apply the mirror equation: 1/s + 1/s’ = 2 /R
Where: s = 4 cm, which is positive (to left of mirror). Also, we have R = 12 cm. Then we need to find s’ the image distance:
1/s’ = 2/ R – 1/s = 2/12 – ¼ = 1/6 – ¼
For which s’ = -12 cm
The negative sign denotes a virtual image which lies to the right of the mirror and this situation can be depicted as shown below:
The magnification of the image is just: M = s’/s = h’/ h
So:
M = ï s’/s ï = ï -12cm /4 cm ï = 4
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