A spherical lens is used to obtain an image on a screen. The size of the image is four times and size of the object . What is the type of lens and at what distance is the screen placed from the lens ?

Explanation

Data : `M=-4`, type of lens ? V=?
As the iamge formed by the lens is obtained on a screen , it is a real image. The lens is , therefore, a convex lens.
`M=-4 v/u therefore u=-v/4`
`1/f =1/v- 1/u=1/v-(1)/((-v//4))=1/v+(4)/(v)=(5)/(v)`
`therefore v=5f`
The distance of the screen from the lens =5f.