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A peson looks into a spherical mirror. T...

A peson looks into a spherical mirror. The size of image of his face is twice the actual size of his face. If the face is at a distance of 20cm, then find the radius of curvature of the mirror.

Text Solution

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The person will see his face only when the image is virtual. Virtual image of a real object is erect. Therefore,
`m=2`
`:.(-v)/(u)=2 (" Here " u = -20 cm)`
`rArr v=40cm`
Applying `(1)/(4)+(1)/(u)=(1)/(f), f=-40cm` or `R=80 cm`.
Aliter : `m=(f)/(f-u)`
`rArr 2=(f)/(f-(-20)) rArrf=-40 cm` or `R=80 cm`.
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