The distance between an object and its 3 times magnified virtual image produced by a convex lens is 20 cm. The focal length of the lens used i s ______ cm.

Question

G1 Physics · Accepted Answer

For a virtual image with magnification 3, using magnitudes: v = 3u The separation is: v - u = 20 cm 2u = 20 u = 10 cm, v = 30 cm Using Cartesian signs, u = -10 cm and v = -30 cm. Lens formula: 1/f = 1/v - 1/u = -1/30 + 1/10 = 1/15 f = 15 cm