In an experiment to find the focal length of a concave mirror a graph is drawn between the magnitudes of u and v. The graph looks like

In case of concave mirror, when we move the object from infinity to focus of the mirror (i.e., u decreases from $\infty$ to f) the image moves from focus to $\infty$ (i.e., v increases from f to $\infty$). Therefore, the graph looks like the curve shown in Fig. (3).