Question

A pin 2 cm long is placed 12 cm away from a convex lens at right angles to the principal axis. If the focal length of the lens is 20 cm, by scale drawing find the size of the image and its magnification.

Answer 1

Given O = 2 cm, u = 12 cm, f = 20 cm

I = ?,   M = ?

Taking the scale of measurement are : 2 cm = 1 cm on the graph.

In the drawing,

O = 1cm, u = 6cm, f = 10 cm

From the drawing,

I = 2.7 cm

⇒ actual image size I = 2.7 x 2 = 5.4 cm

Magnification m = `"I"/"O" = 5.4/2` = 2.7 cm