A lens forms a real image of an object. The distance from the object to the lens is x cm and that from the lens to the image is y cm. The graph shows the variation of y with x.
It can be deduced that the lens is

Options

A. converging and of focal length `10 cm`.
B. converging and of focal length `20cm`.
C. converging and of focal length `40cm`
D. diverging and of focal length `20 cm`

Answer

A

Explanation

A diverging lens if ruled out because both `x` and `y` are positive values. Both `x` and `y` equal `20cm` at their smallest sum, which occurs when
`x+y=40cm=40f`
`:. f=10 cm`
This indicates a converging lens of focal length.
`=10 cm`