Geometrical Optics

A 2 meter long scale with least count of \(0.2 \mathrm{~cm}\) is used to measure the locations of objects on an optical bench. While measuring the focal length of a convex lens, the object pin and the convex lens are placed at \(80 \mathrm{~cm}\) mark and \(1 \mathrm{~m}\) mark, respectively. The image of the object pin on the other side of lens coincides with image pin that is kept at \(180 \mathrm{~cm}\) mark. The \(\%\) error in the estimation of focal length is: