Final answer:
When a convex lens (converging lens) and a concave lens (diverging lens) are combined, a real image can be formed if the convex lens has a greater focal length than the concave lens and the object is placed outside the combined focal length of the system, which must be positive.
Step-by-step explanation:
The assertion states that a combination of a convex lens and a concave lens forms a real image when the focal length of the convex lens is greater than that of the concave lens. In physics, a convex lens, being a converging lens, can form real or virtual images depending on the position of the object relative to its focal length (f). For real images to be formed by a convex lens, the object distance (do) must be greater than the focal length of the lens (do > f) and the focal length must be positive. This scenario is known as a case 1 image.
On the other hand, a concave lens, which is a diverging lens, only forms virtual images, which are always right-side up and smaller than the actual object, referred to as case 3 images. However, when used in combination and the focal length of the convex lens exceeds that of the concave lens, the concave lens has the potential to reduce the overall power of the system, thus allowing a real image to be formed if the object is placed appropriately outside the combined focal length of the lens system.
Real images are inverted and can be projected onto a surface, such as in cameras and projectors. The presentation of a real image is indicative of the combined focal length being effectively less than the object distance (do > combined f), which can occur when the focusing power of the convex lens supersedes the diverging effect of the concave lens.