tailieunhanh - John Wiley And Sons Electronics For Dummies Ebook P2

Getting Started in Electronics plant, the direction in which the electrons flow changes 120 times a second, making a complete turnaround 60 times a second. This change in electron flow is called alternating current, or AC. When the change in electron flow makes a complete loop, it’s called a cycle. The number of cycles per second in alternating current is measured in Hertz, abbreviated Hz. The example of a cycle in the previous paragraph is based on the fact that the United States uses a 60 Hertz standard frequency; some other countries use 50 Hertz as a standard, which means that. | 14 Part I Getting Started in Electronics plant the direction in which the electrons flow changes 120 times a second making a complete turnaround 60 times a second. This change in electron flow is called alternating current or AC. When the change in electron flow makes a complete loop it s called a cycle. The number of cycles per second in alternating current is measured in Hertz abbreviated Hz. The example of a cycle in the previous paragraph is based on the fact that the United States uses a 60 Hertz standard frequency some other countries use 50 Hertz as a standard which means that the electrons change direction 100 times a second. Electricity generated at a dam uses water to turn a coil of wire inside a huge magnet. One of the properties of magnets and wires is that when you move a wire near a magnet a flow of electrons is induced in the wire. First the magnet causes the electrons to flow in one direction and then when the wire loop rotates 180 degrees the magnet pulls the electrons in the other direction. This rotation creates alternating current. Just plugging a cord into a wall outlet sounds easy enough but you need direct current for most projects rather than alternating current. If you use wall outlets to supply electricity for your project you have to convert the electricity from AC to DC. You can do this conversion with something called a power supply. For an example of a power supply think of the charger that you use for your cell phone this little device essentially converts AC power into DC power that the battery uses to charge itself back up. You can find out more about power supplies in Chapter 3. Safety safety safety. It s an important issue for you to consider when deciding whether to use the AC electricity that you get from wall outlets. Using the electricity from a battery is like petting a house cat. Using the electricity from wall outlets is more like cozying up to a hungry lion. With a cute tabby you may get your hand scratched with the king .