Fundamental Principle: Refraction vs. Reflection
The core difference lies in how these optical devices interact with light. A lens manipulates light by **refraction**, bending light rays as they pass through its transparent material. In contrast, a mirror functions by **reflection**, bouncing light rays off its polished, opaque surface.
Light Manipulation and Image Formation
Lenses form images by converging or diverging light rays that *pass through* them; for instance, a convex lens brings parallel rays to a focal point, while a concave lens spreads them out. Mirrors, on the other hand, form images by reflecting light *in front of* or *behind* their surface. A concave mirror converges reflected light, whereas a convex mirror diverges it.
Practical Examples and Everyday Applications
Common examples of devices using lenses include eyeglasses, cameras, microscopes, and refracting telescopes, all requiring light to traverse the medium. Mirrors are found in items like periscopes, car side-view mirrors, shaving mirrors, and reflecting telescopes (e.g., the Hubble Space Telescope), where light needs to be redirected or focused from a single side.
Nature of Images Produced
Lenses can produce both real images (which can be projected) and virtual images (which cannot) on either side, depending on the object's distance relative to the focal point. Mirrors also produce real images (concave mirrors for distant objects) or virtual images (flat mirrors, convex mirrors, or concave mirrors for close objects), but real images are formed on the same side as the object, while virtual images appear to be behind the reflective surface.