Experiment 25: MagnetismChapter 5236Experiment 25: MagnetismThis experiment should be a part of any school science class, but even if you remember doing it, I suggest that you do it again, because setting it up takes only a matter of moments, and it’s going to be our entry point to a whole new topic: the relationship between electricity and magnetism. Quickly this will lead us into audio reproduction and radio, and I’ll describe the fundamentals of self-inductance, which is the third and final basic property of passive com-ponents (resistance and capacitance being the other two). I left self-inductance until last because it’s not very relevant to the experiments that you’ve done so far. But as soon as we start dealing with analog signals that fluctuate, it becomes essential.You will need:• Large screwdriver.• 22-gauge wire (or thinner). Quantity: 6 feet.• AA battery.ProcedureThis couldn’t be simpler. Wind the wire around the shaft of the screwdriver, near its tip. The turns should be neat and tight and closely spaced, and you’ll need to make 100 of them, within a distance of no more than 2 inches. To fit them into this space, you’ll have to make turns on top of previous turns. If the final turn tends to unwind itself (which will happen if you’re using stranded wire), secure it with a piece of tape. See Figure 5-11.Now apply a battery, as shown in Figure 5-12. At first sight, this looks like a very bad idea, because you’re going to short out your battery just as you did in 24,Experiment 2. But by passing the current through a wire that’s coiled instead of straight, we’ll get some work out of it before the battery expires.Put a small paper clip near the screwdriver blade, on a soft, smooth surface that will not present much friction. A tissue works well. Because many screw-drivers are already magnetic, you may find that the paper clip is naturally attracted to the tip of the blade. If this happens, move the clip just outside the range of attraction. Now apply the 1.5 volts to the circuit, and the clip should jump to the tip of the screwdriver. Congratulations: you just made an electromagnet.Figure 5-12. A schematic can’t get much simpler than this.FundAmentAlsAtwo-wayrelationshipEvery electric motor that was ever made uses some aspect of the relationship between electricity and magnetism. It’s absolutely fundamental in the world around us. Remember that electricity can create magnetism: When electricity flows through a wire, it creates a magnetic force around the wire.The principle works in reverse: mag-netism can create electricity. When a wire moves through a magnetic field, it creates a flow of electricity in the wire.This second principle is used in power generation. A diesel engine, or a water-powered turbine, or a windmill, or some other source of energy either turns coils of wire through a powerful magnetic field, or turns magnets amid some massive coils of wire. Electricity is induced in the coils. In the next experiment, you’ll see a dramatic mini-demo of this effect.Figure 5-11. Anyone who somehow missed this most basic childhood demo of electro-magnetism should try it just for the fun of proving that a single AA battery can move a paper clip.