How can a converging lens produce a virtual image?

When the object is close to a convex lens (closer than the focal length of the lens), the lens behaves as a magnifying glass.

A virtual image is one which cannot be formed on a screen as the rays of light do not actually meet after passing through the lens. This happens when the object is closer to the lens than its focal length.

The lens is not powerful enough to bring the light to a focus behind it, so to see the image you have to look through the lens. The image formed will be erect (the same way up as the object), virtual and magnified.

The closer to the focal length the object is the greater the magnification will be. This is why magnifying glasses only when they are placed at the right distance from the object being viewed.