Electronica.pdf
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This document is the copyright page and table of contents for the book "Electronics All-in-One For Dummies®, 2nd Edition". It lists John Wiley & Sons as the publisher and copyright holder. The table of contents provides an overview of the book's 5 sections and 37 chapters, which cover topics ranging from basic electricity and electronics concepts to building circuits with components like resistors, capacitors, transistors, integrated circuits, and working with digital logic.
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Electronica.pdf
- 40. Here are some additional points to ponder concerning voltage: Whenever there’s a difference in charge between two locations, there’s a possibility that a current will flow between the two locations if those locations are connected by a conductor. Because of this possibility, the term potential is often used to describe voltage. Without voltage, there can be no current. Thus, voltage creates the potential for a current to flow. If current can be compared to the flow of water through a hose, voltage can be compared to water pressure at the faucet. It’s water pressure that causes the water to flow in the hose. V oltage is measured using a unit called, naturally, the volt , usually abbreviated V. The voltage that’s available in a standard electrical outlet in the United States is about 117 V . The voltage available in a flashlight battery is about 1.5 V . A car battery provides about 12 V . You can find out how much voltage exists between two points by using a device known as a voltmeter , which has two wire test leads that you can touch to different points in a circuit to measure the voltage between those points. Figure 2-3 shows a typical voltmeter. (Actually, the meter shown in the figure is technically called a multimeter because it can measure things other than voltage. For more information about using a voltmeter, refer to Chapter 8 of this minibook.) V oltages can be considered positive or negative, but only when compared with some reference point. For example, in a flashlight battery, the voltage at the positive terminal is relative to the negative terminal. The voltage at the negative terminal is relative to the positive terminal. I’d like to tell you the exact definition of a volt, but I can’t — at least not yet. The definition of a volt won’t make any sense until you learn about the concept of power , which is described later in this chapter in the section titled “Understanding Power .” Although current stops flowing when the two sides of the circuit have been neutralized, the electrons in the circuit don’t stop moving. Instead, they simply revert to their natural random movement. Electrons are always moving in a conductor. When they get a push from a voltage, they move in the same direction. When there’s no voltage to push them along, they move about randomly. In electrical equations, voltage is usually represented by the letter E , which stands for electromotive force .
- 44. watt is the amount of work done by a circuit in which one ampere of current is driven by one volt. This relationship lends itself to a simple equation. I promised myself when I started this book that I would use as few equations as possible, but I knew I’d have to include at least some of the basic equations. Fortunately, this one is pretty simple: In other words, power (P) equals voltage (E) times current (I). To use the equation correctly, you must make sure that you measure power, voltage, and current using their standard units: watts, volts, and amperes. For example, suppose you have a light bulb connected to a 10-volt power supply, and one-tenth of an ampere is flowing through the light bulb. To calculate the wattage of the light bulb, you use the formula like this: Thus, the light bulb is doing 1 watt of work. Often, you know the voltage and the wattage of the circuit and you want to use those values to determine the amount of current flowing through the circuit. You can do that by turning the equation around, like this: For example, if you want to determine how much current flows through a lamp with a 100-watt light bulb when it’s plugged into a 117-volt electrical outlet, use the formula like this: Thus, the current through the circuit is 0.855 amperes. Here are some final thoughts concerning the concept of power: The term dissipate is often used in association with power. As the energy carried by an electric current is converted into another form such as heat or light, the circuit is said to dissipate power. Did you notice that current and voltage are represented by the letters I and E, not the letters C or V as you might expect, but power is represented by the letter P? Sometimes you wonder if the people who make the rules are just trying to confuse everyone. Maybe the following table will help you keep things sorted out: Concept Abbreviation Unit Current I amp (A) Voltage E or EMF volt (V) Power P watt (W) Earlier in this chapter, in the section “Understanding V oltage ,” I say that I can’t define “one volt” until you know what power is. Now that you know, you can see that the definition of a volt is simple: One volt is the amount of electromotive force (EMF) necessary to do one watt of work at one
- 45. ampere of current. The formula is sometimes called Joule’s Law , named after the person who discovered it. This little factoid will not be on the test. Calculating the power dissipated by a circuit is often a very important part of circuit design. That’s because electrical components such as resistors, transistors, capacitors, and integrated circuits all have maximum power ratings. For example, the most common type of resistor can dissipate at most watt. If you use a -watt resistor in a circuit that dissipates more than watt of power, you run the risk of burning up the resistor.