Practice question

**Refraction at spherical surface** formula n₁/u + n₂/v = (n₂-n₁)/R governs single surface, extension to two surfaces yields lens maker. Double convex with equal |R| has f = R/[2(n-1)], for R=12 cm, n=1.5, f=12 cm, illustrating dependence on curvature and index. A convex mirror always forms a virtual, erect, and diminished image. As the object moves closer, the image size increases slightly but remains diminished (less than the object size), and the image distance increases, approaching the focal length as a limit, though it never exceeds it. Substituting values gives Image size increases but remains diminished, which matches expected image position and magnification from mirror/lens