In a convex lens, if the object is placed at 2F (twice the focal length), the image formed will be:
- AReal, at 2F and of the same size as the object
- BVirtual, at F and magnified
- CReal, at 2F and magnified
- DVirtual, beyond 2F and diminished
Show answer and explanation
Correct answer: (a) Real, at 2F and of the same size as the object
Explanation
For a convex lens with the object at 2F, the image is formed at 2F on the other side. It is real, inverted and the same size as the object.
By the lens formula (1/v − 1/u = 1/f), u = −2f gives v = +2f, and the magnification v/u = −1: the same size, inverted.
For other positions: beyond 2F, the image is between F and 2F and diminished; between F and 2F, it is beyond 2F and magnified; between F and the lens, it is virtual, erect and magnified.