Practice portal › Ray Optics and Optical Instruments › Reflection by Plane and Spherical Mirrors
Asked in GSEB Board March 2022 · Mirror formula and magnification
Given: u=-15 cm and, for a concave mirror, R=-20 cm, so f=R/2=-10 cm.
Idea: the mirror formula 1/v+1/u=1/f, with distances measured from the pole and against the incident light taken negative.
1/v=1/f-1/u=-1/(10)+1/(15).
Over the common denominator 30: 1/v=(-3+2)/(30)=-1/(30).
So v=-30 cm: a real image 30 cm in front of the mirror.
That is the expected behaviour — the object lies between f and 2f, so the image forms beyond 2f and is magnified.
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