Question

Question 3
Where should an object be placed in front of a convex lens to get a real image of the size of the object?

(a) At the principal focus of the lens
(b) At twice the focal length
(c) At infinity
(d) Between the optical centre of the lens and its principal focus

Answer 1

(b) At twice the focal length

The object should be placed at twice the focal length in front of a convex lens to get a real image of the size of the object.

Also since v = u,
magnification $m=\frac{v}{u}=1$
m = 1 implies that size of the image is same as that of size of the object.