Electricity can seem contradictory. A light bulb is a smaller version of an immersion heater but in a different environment. It’s almost incidental that a bulb filament sheds light since its initial function is to resist the flow of electricity. In doing this it becomes hot. So hot that it glows.A lit bulb is – not unnaturally – said to be working. The bulb’s work capacity and work rate (and that of many other things from humans to cars) are measured in Watts or Watt-hours. As explained earlier (“Why electricity and water don’t mix”, May 13) to understand this better requires some maths. Bad news!
However, despite electricity’s invisibility and its intellectual obscurity its ability to “work” can be physically sensed. A bike dynamo would do but would be clumsy. Rather better is the hand-generator found in school physics labs – probably not these days since such things were lethal in the hands of mischievous schoolboys.
Turn the generator and it rotates quite freely. Attach a resistance (it could be a light bulb) across the output and the handle is now harder to turn. Evidence of electrical work.
