Question

A point object is placed at a distance of `20cm` from a thin plano-convex lens of focal length `15cm`If the plane surface is silvered.the image will form at

A. `60cm`left of `AB`
B. `30cm`left of `AB`
C. `12cm`left of `AB`
D. `60cm`Right of `AB`

Answer 1

Correct Answer - C
`P_(eq)=2P_(l)+P_(m) rArr P_(eq)=2P_(l)`
`P_(eq)=(200)/(15) rArr P_(eq)=(40)/(3)`
`f_(eq)=-(100)/(P_(eq))rArrf_(eq)=-(100)/(40)xx3`
`f_(eq) =(-15)/(2)"cm"`
Applying mirror formula
`(1)/(v)+(1)/(u)=(1)/(f)rArr (1)/(v)+(1)/(-20)=(2)/(-15)`
`(1)/(v)=-(2)/(15)+(1)/(20) rArr (1)/(v)=(-8+3)/(60)`
`v=-12cm`
Image will be `12cm`left of `AB`