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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
(b) At twice the focal length
Explanation
A convex lens produces an image of the same size
when the object is placed at twice the focal length.
This image is real and inverted.
