Question

What is the focal length of a lens that produces a real image three times as large as the object if the distance between image and object is 1.0m?​

Answer 1

Answer:

Ans: 18.75 cm

Explanation:

Magnification = v /u = -3 (real and inverted image)

                 v = -3u ........eq (2)

Focal length 1/f = 1/v - 1/u  ......eq (3)

Substitute eq (2) in eq (1), we get u=-25 cm

eq (2) v = -3 u cm. = - 3 *- 25 = 75 cm

Substitute eq (2) in eq (3), we get f = - 3 u/4 = -3 * -25/4 = 18.75