Question

A convex lens with focal length 9 cm forms an image of an object placed 21 cm to the left of the lens. what is the distance to the image formed?

Answer 1

15.75 cm

Step-by-step explanation:

focal length of convex lens, f = + 9 cm

position of object, u = - 21 cm

Let the distance of image is v.

Use lens equation

1 / f = 1 / v - 1 / u

1 / 9 = 1 / v + 1 / 21

1 / v = 1 / 9 - 1 / 21 = (21 - 9) / (21 x 9)

1 / v = 12 / 189

v = 15.75 cm