Question

If an object be placed at a distance of 60cm from a convex lens of a focal length 20cm, a real image is formed behind the lens. Obtain the position of the image and its magnification.​

Answer 1

Given:

An object is placed at a distance of 60 cm from a convex lens of a focal length of 20 cm.

To Find:

The position of the image formed and the lens' magnification.

Formula:

We know that, 1/v + 1/u = 1/f, and magnification = v/u .

Solution:

Object distance (u) = 60 cm

Focal length (f) = 20 cm

1/v + 1/u = 1/f

or, 1/v = 1/f - 1/u

or, 1/v = 1/20 - 1/60

or, 1/v = 1/30

or, v = 30 cm

Magnification = v/u

ﾠﾠﾠﾠﾠﾠﾠﾠﾠﾠﾠﾠ= 30/60

ﾠﾠﾠﾠﾠﾠﾠﾠﾠﾠﾠﾠ= 1/2

Answer:

The image distance is 30 cm, and the magnification by the lens is 1/2 .