Question

When an object is placed 10 cm in front of lens A, the image is real, inverted, magnified and formed at a great distance. When the same object is placed 10 cm in front of lens B, the image formed is real, inverted and same size as the object. 

What is the focal length of lens B?

Answer 1

The focal length of lens B is 5 cm as only a converging lens forms a real, inverted and same size image of object when the object is placed at 2F position of the lens.