Читать книгу Electronics All-in-One For Dummies - Lowe Doug, Doug Lowe - Страница 12

Before you can understand even the simplest concepts of electronics, you must first understand what electricity is. After all, the whole purpose of electronics is to get electricity to do useful and interesting things.

The concept of electricity is both familiar and mysterious. We all know what electricity is or at least have a rough idea based on practical experience. In particular, consider these points:

 We are very familiar with the electricity that flows through wires like water flows through a pipe. That electricity comes from power plants that burn coal, catch the wind, absorb sunlight, or harness nuclear reactions. It travels from the power plants to our houses in big cables hung high in the air or buried in the ground. Once it gets to our houses, it travels through wires through the walls until it gets to electrical outlets. From there, we plug in power cords to get the electricity into the electrical devices we depend on every day, such as ovens and toasters and vacuum cleaners.

 We know, because the electric company bills us for it every month, that electricity isn’t free. If we don’t pay the bill, the electric company turns off our electricity. Thus, we know that electricity is valuable.

 We know that electricity can be stored in batteries, which contain a limited amount of electricity that can be used up. When the batteries die, all their electricity is gone.

 We know that some kinds of batteries, like the ones in our cellphones, are rechargeable, which means that when they’ve been drained of all their electricity, more electricity can be put back into them by plugging them into a charger, which transfers electricity from an electrical outlet into the battery. Rechargeable batteries can be filled and drained over and over again, but eventually they lose their ability to be recharged — and you have to replace them with new batteries. (Or, in the case of your iPhone, you have to buy a whole new phone.)

 We also know that electricity is the stuff that makes lightning strike in a thunderstorm. In grade school, we were taught that Ben Franklin discovered this by conducting an experiment involving a kite and a key, which we should not attempt to repeat at home.

 We know that electricity can be measured in volts. Household electricity is 120 volts (abbreviated 120 V). Flashlight batteries are 1.5 volts. Car batteries are 12 volts.

 We also know that electricity can be measured in watts. Traditional incandescent light bulbs are typically 60, 75, or 100 watts (abbreviated 100 W). Microwave ovens and hair dryers are 1,000 or 1,200 watts. The more watts, the brighter the light or the faster your pizza reheats and your hair dries.

 Except that we also know that some technologies do more work for a given wattage. Thus, a 20-watt CFL bulb and a 12-watt LED bulb both produce as much light as a 75-watt incandescent bulb.

 We also may know that there’s a third way to measure electricity, called amps. A typical household electrical outlet is 15 amps (abbreviated 15 A).

 The truth is, most of us don’t really know the difference between volts, watts, and amps. (Don’t worry; by the time you finish Chapter 2 of this minibook, you will!)

 We know that there’s a special kind of electricity called static electricity that just sort of hangs around in the air but can be transferred to us by dragging our feet on a carpet, rubbing a balloon against our hairy arms, or forgetting to put an antistatic sheet in the dryer. And finally, we know that electricity can be very dangerous. In fact, dangerous enough that for almost 100 years electricity was used to administer the death penalty. Every year, hundreds of people die in the United States from accidental electrocutions.