Question

A lens forms a virtual, diminished image of an object placed at 2m from it. The size of image is half of the object. Which one of the following statements is correct regarding the nature and focal length of the lens?
A. Concave, `|f|=1m`
B. Convex, `|f|=1m`
C. Concave, `|f|=2m`
D. Convex, `|f|=2m`

Answer 1

Correct Answer - c.
`m=(f)/(f+u),(1)/(2)=(f)/(f-2),` or `2f=f-2 ` or `f=-2m`
`|f|=2` metre. Since the image is virtual as well as diminshed, therefore the lens is concave.