Final answer:
The main difference between convex and concave lenses is that convex lenses focus light to a point, forming real or magnified virtual images, while concave lenses diverge light, creating only smaller virtual images.
Step-by-step explanation:
The difference between a convex and concave lens pertains to how they refract light. A convex lens, or converging lens, has a thick middle and bends light rays inward, focusing them to a point beyond the lens. This lens can form real or virtual images; real images are inverted, and virtual images are enlarged and upright (case 2 images). On the other hand, a concave lens, or diverging lens, is thinner in the middle and spreads light rays outward, forming only virtual images that are smaller and upright (always case 3 images).
Applications of these lenses include correcting vision problems such as myopia with concave lenses, and hyperopia with convex lenses. Moreover, convex lenses are essential in devices like cameras and slide projectors that need to focus light to create real images, whereas concave lenses help in devices that need to diverge light.