An object is placed at a distance of `f//2` from a convex lens. The image will be

Options

A. At one of the foci, virtual and double its size
B. At `3f//2` , real and inverted
C. At `2f, ` virtual and erect
D. None of these

Answer

A

Explanation

`(1)/(f)=(1)/(v)+(1)/(u)``(` Given `u=(-f)/(2))`
`implies(1)/(f)=( 1)/(v)+((1)/(f//2))implies(1)/(v)=(1)/(f)-(1)/(f)`
`implies (1)/(v)=(-1)/(f)` and `m=(v)/(u)=(f)/(f//2)=2`
So virtual at the focus and of double size.