Question

A beam of light converges towards a point`O`,behind a convex mirror of focal length`20`cm.Find the nature and position of image if the point`O`is-
(1) `10`cm behind the mirror, (2) `30`cm behind the mirror

Answer 1

Here object is virtual
(1)`u=+10`cm
`f=+20`cm
`v=(uf)/(u-f) rArr v=(10xx20)/(10-20)=-20`cm
magnification `m=-((v)/(u)) m=-((-20)/(10))=+2`
(2) `u=+30cm f=20cm`
`v=(uf)/(u-f) =(30xx20)/(30-20) rArr v=+60cm`
`m=-((60)/(30))=-2`