Question #08234

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Answer 1 · 2017-01-30T16:19:29

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We know the mirror formula as below

$color(blue)(1/v+1/u=2/r)$

where

$u->"object distance"=-20cm$

$v->"image distance"$

$r->"radius of curvature"$

Here it is also given that size of the virtual image seen behind the mirror is twice that of object.This means the magnification $m=-2$

Again $m=v/u=>-2=v/u$

So $v=-2u=-2xx(-20)cm=40cm$

Inserting these values in mirror equation we get

$color(green)(1/v+1/u=2/r)$

$=>1/40+1/-20=2/r$

$=>(1-2)/40=2/r$

$=>r=-80cm$