RELAYS
Y ou might not realize it, but you're constantly on-guard, watching out for threats, ready to act at a moment's notice. Millions of years of evolution have primed your brain to save your skin when the slightest danger threatens your existence. If you're using a power tool, for example, and a tiny wood chip flies toward your eye, one of your eyelashes will send a signal to your brain that make your eyelids clamp shut in a flash—fast enough to protect your eyesight. What's happening here is that a tiny stimulus is provoking a much bigger and more useful response. You can find the same trick at work in all kinds of machines and electrical appliances, where sensors are ready to switch things on or off in a fraction of a second using clever magnetic switches called relays . Let's take a closer look at how they work! Photo: A typical relay with its plastic outer case removed. You can see the two spring contacts on the left and the electromagnet coil (the red-brown...