Where should an object be placed in front of the same convex lens to obtain the same real image the same the same object?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → At twice the focal length.
A convex lens forms an image the same size as the object, real and inverted, only when the object is placed at the centre of curvature, that is at 2F. The image then forms at 2F on the other side of the lens.
An object at infinity gives a point image at the focus, an object at the focus gives an image at infinity, and an object between the optical centre and the focus gives a virtual, erect and magnified image — none of them the same size as the object.