question_answer 3)

Where should an object be placed in front of a convex lens to get a real image of the size of object? (a) At the principal focus of lens (b) At twice the focal length (c) At infinity (d) Between optical centre of lens and its principal focus  

Answer:

(b) To set the real image of the size of the object. It should be placed at twice the focal length of a convex lens.