JEE Main 2008 — Optics

An experiment is performed to find the refractive index of glass using a travelling microscope. In this experiment distance are measured by

A student measures the focal length of 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