The Electromagnetic Spectrum

Hold your hand in front of a television remote control and press a button. Nothing happens. Point the remote at the television across a dark room and the channel changes instantly, with no wire, no sound and nothing at all for your eyes to see. Something crossed that room, carried energy from the little diode in the remote to the sensor on the television, and did it at three hundred million metres every second. It was the same kind of thing that lets you see this page, the same kind of thing that cooks a potato in a microwave oven, the same kind of thing that photographs the bone in a broken wrist. One family, one speed, one continuous spread of possibilities.

This lesson takes that family apart and puts it back in order. You will learn the sequence of the seven regions and what actually changes as you walk along it, why every object in the room around you is glowing in infrared right now and why a matt black surface glows harder than a shiny one, which regions carry our phone calls and our television and why each was chosen, and where along the sequence the radiation stops merely warming you and starts tearing electrons off your molecules. The last part of the lesson stays with X-rays: how a photograph of a bone is possible at all, why the same beam that finds a fracture can be aimed at a tumour, and what a radiographer wears so that a job spent beside an X-ray tube is a safe one.