A convex lens, also known as a converging lens, magnifies objects because it bends light rays inward. When light rays pass through a convex lens, they converge at a point called the focal point. If an object is placed within the focal length of the lens, the light rays diverge after passing through the lens, and the brain perceives this as a larger image of the object. This property of convex lenses makes them useful in devices such as magnifying glasses and cameras.
On the other hand, a concave lens, or diverging lens, has the opposite effect. It spreads out light rays that pass through it. When parallel light rays enter a concave lens, they diverge and appear to come from a virtual focal point behind the lens. This diverging effect causes the image to appear smaller and closer than the actual object. Concave lenses are typically used in glasses for nearsightedness, as they help to correct vision by reducing the size of the image formed on the retina.
In summary, the difference in the shapes and light-bending properties of convex and concave lenses leads to magnification and reduction of object sizes, respectively.