Question

A 4cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20cm. The distance of the object from the lens is 15cm. Find the nature, position and size of the image

Answer 1

Given,
Height of object, h=2.0 cm
Focal length, f= +10 cm
Object distance, u=-15 cm
Using lens formula,
1/v -1/u=1/f
1/v=1/f + 1/u=1/10 - 1/15
v=+ 30 cm
The position of image is at 30 cm on the right side of the lens.
Magnification, m=v/u=30/(-15)=-2
Since the magnification has a negative value, so the image will be real and inverted.
m=h'/h=v/u=-2
h'/2=-2
h'=-4 cm
Height of image is 4 cm.