Question

A convex lens has a focal length of 20 cm. Where should an object be placed in front of this convex lens so as to obtain an image which is real, inverted and same size as the object? Draw the ray diagram to show the formation of image in this case.

Answer 1

When the image formed by a convex lens, inverted and same size as the object, then the distance of the object from the lens is 2f (twice the focal length). Here,
Focal length, f=20 cm
So, `2f= 2 xx 20` cm
=40 cm
Thus, the object should be placed at a distance of 40 cm in front of the convex lens. (Please draw the ray diagram yourself).