Question

A 5 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 30 cm. The distance of the object from the lens is 20 cm. Use lens formula to find the position, size and nature of the image formed.

Answer 1

Given,
Size of object, h=5 cm
Focal length, f=30 cm
Object distance, u=-20 cm
Now, using lens formula
1/v -1/u=1/f
or 1/v=1/f + 1/u
=1/30-1/20
or Image distance, v=-60 cm
Thus, the image is formed on the same side as object.
Magnification, m=v/u=h'/h
m=-60/(-20)=h'/5
m=h'/5=3
or h'=15 cm
The positive sign of magnification and value of h' shows that the image is virtual,erect and enlarged