A 5.0 diopter lens forms a virtual image which is 4 times the object placed perpendicularly on the principal axis of the lens. Find the distance of the object from the lens.

Explanation

`P=5D,m=4,u=-x`
`f=(100)/(P)cm=(100)/(5)=20cm`
`m=(v)/(u)implies4=(v)/(-x)`
`v=-4x`
`(1)/(v)-(1)/(u)=(1)/(f)`
`(1)/(-4x)-(1)/(-x)=(1)/(20)`
`(-1+4)/(4x)=(1)/(20)implies(3)/(4x)=(1)/(20)`
`x=15cm`