Question

The image of an object formed by a lens is of magnification -1, if the distance between the object and its image is 60cm. what is the focal length of the lens?​

Answer 1

Answer:

The magnification of -1 is possible in only convex lens. When the object is moved 20 cm towards the lens, so the new object distance will be = 30 cm - 20 cm = 10 cm. Since the new object distance is less than focal length of the lens, thus the image will be virtual, erect and magnified.