Curved mirrors: concave and convex
Physics · Key Stage 2 · The School
Two curves, two effects
A flat mirror shows a normal, same-size image. A CONCAVE mirror curves INWARD, like the inside of a spoon. Held close, it can MAGNIFY a close-up image. That is why it is used in some make-up and shaving mirrors. A CONVEX mirror curves OUTWARD instead, like the back of a spoon. It shrinks the image, but shows a much WIDER view.
Why a convex mirror shows more
A convex mirror's outward curve spreads reflected light out over a wider angle than a flat mirror could. It packs a much bigger scene into the same size mirror. That is exactly why a car's wing mirror is often slightly convex. It widens the driver's view. But it also makes everything in it look a little smaller and further away than it really is.
Why a concave mirror can magnify
Held close, a concave mirror's inward curve bends reflected light. The image appears larger than the real object. This is useful for shaving, or applying make-up close to the face. Held too far away, though, the same mirror can flip the image upside down instead. A concave mirror behaves quite differently depending on how close you hold it.
A flat mirror shows a face at its normal size, the right way up. A concave shaving mirror, held close, shows the same face noticeably enlarged. It is still the right way up, which is useful for seeing small details clearly. A convex mirror, like a car wing mirror, shows the same face smaller than real life. But it reveals far more of the room behind it too. Three mirrors, three different curves, three genuinely different jobs. A driver relies on knowing that a convex mirror makes things look smaller and further away than they truly are.