Question

Where should an object be placed in front of a convex lens to get a real image the size of the object?
1. At the principal focus of the lens
2. At twice the focal length
3. At infinity
4. Between the optical centre and principal focus of the lens

Answer 1

Answer:

2. At the twice of the focal length

Hope it will help

Answer 2

Answer:

2. At twice the focal length

Explanation:

When the object is placed at the centre of curvature of a lens then a ray of light AO which is parallel to the principal axis after refraction pass through the focus F along the direction OF. While the other ray AC pass through the optical centre C and goes straight without any deviation. These two refracted light rays intersect each other at point A’, on the other side of the lens at the centre of curvature 2F. so, the image A’B’ formed in this case is at the centre of curvature, of same size as the object, real and inverted.