Which type of lens can form an image that may be real or virtual?

• A. Concave lens
• B. Cylindrical lens
• C. Convex lens
• D. Planar lens

Answer: (C)

The ability to form real or virtual images depends on using a converging lens and how far the object is from the lens. A convex lens, which is a converging lens, can produce a real image on the opposite side when the object lies beyond its focal length, because the converging rays actually meet to form a point. If the object is closer than the focal length, the rays don’t meet on the far side; they appear to come from a point on the same side as the object, creating a virtual, upright image that cannot be projected. This dual behavior—real images for distant objects and virtual images for objects inside the focal length—is what makes a convex lens capable of forming either type of image.

A concave lens (diverging) routinely forms only virtual images for real objects, never a real one. A planar lens doesn’t converge rays to form a real image in standard imaging setups. A cylindrical lens focuses in one direction and doesn’t provide the typical real/virtual-image behavior in two dimensions the way a full convex lens does.