In an experiment to find focal length of a concave mirror a graph is drawn. The graph looks like ...........

Options

A.
B.
C.
D.

Answer

A

Explanation

For concave mirror
object distance u, image distance v and focal length f
u = (`alpha`) when v = f
u = 2f (object on centre of curvature)
v = 2f
and when u = f then v = `infty` (infinite)
Second Method:
`t=(uv)/(u+v)` (u+v is constant)
`therefore t prop uv` that means u`alpha 1/v`
So graph C is correct.
These three details are checked by equation `1/f=1/u+1/v`. These three details are satisfied in graph (C) and graph (C) is true for concave mirror.