To find the focal length of a convex mirror, a student records the following data: Object Pin Convex Lens Convex Mirror Image Pin 22.2 cm 32.2 cm 45.8 cm 71.2 cm The focal length of the convex lens is f1 and that of mirror is f2. Then taking index correction to be negligibly small, f1 and f2 are close to :

Applying the lens equation, we get1v+110=1f1... (1)For mirror,125.4𕒵45.8󔼨.2−v=1f2125.4𕒵13.6−v=1f2 (2)Since there are 3 variables and only two equations (1) and (2) therefore only by substitutingf1 f2from options correct values can be verified.Eliminatingvfrom the equation (1), we get a relation betweenf1andf2. This relation is satisfied only by option A.