A concave mirror forms a real image with magnification −2. The object-image separation is 30 cm. Find |f| in centimetres.
Physics · Geometrical optics · spherical mirror
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Question

A concave mirror forms a real image with magnification −2. The object-image separation is 30 cm. Find |f| in centimetres.

G1 Physics · Accepted Answer

For a real image v=2u in magnitude. Separation v−u=u=30 cm, so u=30 and v=60 cm. Thus f=uv/(u+v)=20 cm.