For a concave mirror, two conjugate real-object positions are 20 cm and 60 cm from the pole. Find |f| in centimetres.
Physics · Geometrical optics · spherical mirror
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Question

For a concave mirror, two conjugate real-object positions are 20 cm and 60 cm from the pole. Find |f| in centimetres.

G1 Physics · Accepted Answer

The two positions are conjugate: f=uv/(u+v)=20×60/80=15 cm.