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1、Chapter 1 Electric and Electronic Technology Fundamentals,Unit 1 Electric Elements and Components,Text,New Words and Expressions,Exercises,End,Unit1 Electric Elements and Components,Introduction Electrical elements are conceptual abstractions used in the analysis of electrical networks. Any electric
2、al network can be analyzed as multiple, interconnected electrical elements in a schematic diagram or circuit diagram, each of which affects the voltage in the network or current through the network.These ideal electrical elements represent real, physical electrical or electronic components but they
3、do not exist physically and they are assumed to have ideal properties according to a lumped element model, while components are objects with less than ideal properties, a degree of uncertainty in their values and some degree of nonlinearity, each of which may require a combination of,multiple electr
4、ical elements in order to approximate its functions. Circuit analysis using electric elements is useful for understanding many practical electrical networks using components. By analyzing the way a network is affected by its individual elements it is possible to estimate how a real network will beha
5、ve.,Unit1 Electric Elements and Components,The elements The four fundamental circuit variables are current, I; voltage, V, charge, Q; and magnetic flux, . Only 5 elements, produced by manipulating these four variables, are required to represent any component or network in a Linear system. Two source
6、s: Current source, measured in amperes - produces a current in a wire. An ideal current source is a mathematical model, which real devices can only approach in performance. The current through an ideal current source is independent of the voltage across it.,Unit1 Electric Elements and Components, Vo
7、ltage source, measured in volts - produces a potential difference across two points. An ideal voltage source is only exists in mathematical models of circuits. Similarly, the voltage across an ideal voltage source is independent of the current through it. Three passive elements: Resistance R, measur
8、ed in ohms - produces a voltage proportional to the current flowing through the element. Relates voltage and current according to the relation Capacitance C, measured in farads - produces a current proportional to the rate of change of voltage across the element. Relates charge and voltage according
9、 to the,Unit1 Electric Elements and Components,relation,Unit1 Electric Elements and Components,., Inductance L, measured in henries - produces a voltage proportional to the rate of change of current through the element. Relates flux and current according to the relation,.,The Components A battery pr
10、ovides electromotive force (emf), or voltage, in a circuit. It contains layers of chemicals that cause electrons to move in a certain direction, from its negative pole to its positive pole. It is marked with a rating of how much voltage there is across the two poles, and a (-) for the negative pole
11、and a (+) for the positive pole. Batteries may also be marked with an ampere hour (Ah) rating, indicating total charge capacity. An ideal battery can thus be represented as a voltage source. In practice, a battery also has an internal resistance that is represented as a resistance in series with the
12、 voltage source.,Unit1 Electric Elements and Components,If a wire is used to connect the two poles of a battery, electrons flow through the wire from the negative end to the positive end. (The wire will also get hot because it isnt a perfect conductor, and the battery will quickly exhaust all its po
13、wer.) Thus a wire can be represented as a low-value resistor. Current sources are often absent from basic electric circuits, and are more likely to be found in electronic circuits containing semiconductors. For example, on a first degree of approximation, a bipolar (junction) transistor may be repre
14、sented by a variable current source that is controlled by the input voltage.,Unit1 Electric Elements and Components,A resistor is a component whose function is to regulate the current in the circuit. One common kind is a little cylinder of graphite with metal wires coming out of either end. These ar
15、e painted with colored stripes that indicate the resistance, in ohms, and the tolerance, in percent. This system is called the resistor color code. Another kind of resistor is a filament, which is a coil of metal wire that can withstand high temperature but has a finite resistance. When a current is
16、 passed through a filament, it heats up because of this resistance. Filaments are commonly used in light bulbs and heaters. They are marked with the voltage that should be applied to them, and the power, in watts, that they will then give off as light and heat. Due to the effect of heating, a filaments resistance is higher when it is hot than when it is cold.,Unit1 Electric Elements and Components,An electric charge can be stored and then quickly released by a co
