Question

An object 4 cm high is placed at a distance of 10cm from a convex lens of focal length 20cm. find the position, nature and size of image

Answer 1

The position of the image is 20 cm.

The image is virtual and magnified.

How to calculate the position of the image?

The position of the image is calculated by applying the following lens formula as shown below;

1/f = 1/v + 1/u

where;

• f is the focal length of the lens
• v is the image distance
• u is the object distance

1/20 = 1/v + 1/10

1/v = 1/20 - 1/10

1/v = (1 - 2)/20

1/v = -1/20

v = - 20 cm

The image formed is a virtual image.

The size of the image formed is calculated as;

M = v / u

M = (20 cm ) / 10 cm

M = 2

Height of the image = 2 x 4 cm = 8 cm