A student measures the focal length of a convex lens by putting an object pin at a distance `u` from the lens and measuring the distance `v` of the image pin. The graph between `u` and `v` plotted by the student should look like

Options

A.
B.
C.
D.

Answer

C

Explanation

For a convex lens
`u=-ve f=+ve`
If `v=infty, u=f` and if `u=-infty, v=-f` .
We have `v=+ve` and `u=-ve`
and `u` and `v` are symmetrical. Hence graph is shown,