10.1 Spherical Mirrors
The Magic Mirrors
At a science centre, Meena peered into a row of curved mirrors. In one, her face looked hugely enlarged; her brother, a little farther back, appeared upside down! In another, she saw a tiny version of herself. She was baffled — in an ordinary mirror, her image was always the same size and the right way up. The guide smiled: “These aren’t plane mirrors — they’re spherical mirrors, curved inward or outward.”
You don’t need a science centre to see this — a shiny spoon will do.
Activity 10.1 — The two faces of a spoon Hold the inner (curved-in) side of a shiny spoon near your face: your image is inverted (upside down). Flip it and look at the outer (bulging-out) side: now your image is erect but smaller. The spoon is acting as a curved mirror — and which way it curves changes everything.
Concave and Convex A spherical mirror has a reflecting surface shaped like part of a hollow sphere.
- A concave mirror curves inward (like the inner spoon, or a cave) — its reflecting surface is the inside of the curve.
- A convex mirror curves outward (like the back of the spoon) — its reflecting surface bulges toward you.
A Step Further: How They’re Made Spherical mirrors aren’t cut from a glass ball — they’re made by grinding and polishing flat glass into a curved shape, then adding a reflective coating (a thin layer of aluminium). Coat the outer curve → a concave mirror; coat the inner curve → a convex mirror.
Activity 10.2 — Tell them apart Lay both mirrors face-up and look across them from the side, at eye level. The one that dips inward is concave; the one that bulges outward is convex. (You can also tell them apart by the images they form — coming up next!)