that use this energy and change it to useful work) and the wires which go to load and returns back to the source. Normally you can see it in the form of a block diagram. It consists of a source of electrical energy, some sort of load to make use of that energy, and electrical conductors connecting the source and the load. The electrical source has two terminals, designated positive (+) and negative (-). As long as there is an unbroken connection from source to load and back again electrons will be pushed from the negative terminal of the source, through the load, and then back to the positive terminal of the source. Water is the best example of this process. You have a quantity of water which from Higher level (for electricity, higher voltage) goes to lower level as a cascade (electricity, lower voltage level) and during this operation, he does some kind of useful work for us. When ever the electrons do always moving in the same direction through the circuit, their motion is known as a direct current (DC). The source can be any source of electrical energy. In practice, there are three general possibilities: it can be a battery, an electrical generator, or some sort of electronic power supply. The load is any device or circuit powered by electricity. It can be as simple as a light bulb or as complex as a modern high-speed computer. ________________________________________ The electricity provided by the source has two basic characteristics, called voltage and current. These are defined as follows: Voltage The electrical "pressure" that causes free electrons to travel through an electrical circuit. Also known as electromotive force (emf). It is measured in volts. Current The amount of electrical charge (the number of free electrons) moving past a given point in an electrical circuit per unit of time. Current is measured in amperes. ________________________________________ The load, in turn, has a characteristic called resistance. By definition: Resistance That characteristic of a medium which opposes the flow of electrical current through itself. Resistance is measured in ohms. ________________________________________ The relationship between voltage, current, and resistance in an electrical circuit is fundamental to the operation of any circuit or device. Verbally, the amount of current flowing through a circuit is directly proportional to the applied voltage and inversely proportional to the circuit resistance. By explicit definition, one volt of electrical pressure can push one ampere of current through one ohm of resistance. Two volts can either push one ampere through a resistance of two ohms, or can push two amperes through one ohm. Mathematically, E = I × R, where E = The applied voltage, or EMF I = The circuit current R = The resistance in the circuit
necessary to distinguish between them in any circuit diagram. Of course, we could use the block diagram approach, and just identify each component with words. Unfortunately, this takes up a lot of space and makes the overall diagram harder to recognize or understand quickly. We need a way to understand electrical diagrams far more quickly and easily. The answer is to use schematic symbols to represent electronic components, the symbols define exactly what this circuit is and how it behaves. ________________________________________ The symbol for each electronic component is suggestive of the behavior of that component. Thus, the battery symbol above consists of multiple individual cells connected in series. By convention, the longer line represents the positive terminal of each cell. The battery voltage would normally be specified next to the symbol. The zig-zag line represents any resistor. In most cases, its resistance is specified next to the symbol just as the battery voltage would be given. It is easier and faster to read the symbol and the legend "4.7k" next to it, than to see a box and have to read "4700-ohm resistor" inside it. As we introduce various electronic components in these pages, we will provide their schematic symbols as well. ________________________________________ One of the problems that can occur with schematic diagrams is too many lines all over the page. It's not a big deal when there are only two components in the circuit, but think of what the complete diagram for a modern television receiver or even a radio receiver would look like. We need a way to reduce the number of lines showing electrical connections. We can help reduce the problem by noting that one connection is common to all circuitry, and serves as the reference point from which all electrical measurements are made. This electrical connection is designated the "ground reference," or simply "ground," in the circuit. The modified schematic diagram is shown to the right. This circuit is actually the same as the one above, with the voltage source designated "E" (for EMF or ElectroMotive Force) and the load designated "R" (for Resistance). The ground symbols ( ) are assumed to be electrically connected to each other without any explicit connection shown. Often a circuit will be constructed on a steel or aluminum chassis, in which case the chassis itself is commonly used as the electrical ground as well as the mechanical support for the circuitry. |
| Basic Electrical Circuit. |
| What Electrical Circuit Is Composed of? |
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