Question

A convergent lens has a focal length of 15 cm. At what distance should an object from the optical centre of the lens be placed so that its real image is formed at 30 cm on the other side of the lens?

Answer 1

Object distance = 30 cm

Explanation:

A convergent lens is a concave lens. Given focal length (f) is 15 cm and image distance (v) is 30cm on the other side of the lens.

To find object distance (u), we can use the lens formula: 1/v - 1/u = 1/f

In a concave lens, the focal length and image distance are negative. So we get:

-1/10 -1/u = -1/15

1/u = 1/10 - 1/15

1/u = (-10 + 15) / 150 = 5/150 = 1/30

Therefore u = 30 cm