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Introduction |
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Appliances used in our day to day life are based on the principles of electricity and magnetism. Electricity is one of the most important sources of energy. Lights, fans, motors, radios and television are some common appliances which work on electricity. |
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Potential and Potential Difference |
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'Electrical potential' is a condition, which determines the direction of the flow of charge. |
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Electrostatic Potential |
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The electrostatic potential is defined as the work done in bringing a single positive charge from infinity to a point (Any point outside the electric field or space is called infinite point). The unit of potential is volt (symbol V). |
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Electric Current |
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If two charged bodies of different potential are placed one beside the other, the charges will not move from one body to the other. But if the two bodies are connected using a conductor, the flow of charges takes place. Charges will flow as long as there is potential difference between the two bodies. This rate of flow of electric charge is called 'electric current'. |
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Sources of Electricity |
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Batteries produce electricity by converting chemical energy into electrical energy. Batteries provide electricity to torches, transistors, toys, clocks and watches. |
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Electric Circuits and their Components |
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The devices which deliver electricity are called the 'sources'. Lamps, electric engines, etc. which consume electricity are called ‘loads’. Switches are used to switch the loads on and off whenever necessary. Hence, the source, the loads, and the switches are connected to form electrical circuits. |
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Ohm's Law |
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In the year 1820 a French physicist, Andre Ampere made many discoveries on the nature of electricity. While a German physicist, Georg Ohm showed that the flow of an electric current through a wire depended on its 'resistance' and the potential difference between its ends. |
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Conductors and Insulators |
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Substances which do not allow electricity to pass through them easily are called insulators. These are made from materials which have a high resistance. Some substances which are insulators are air, plastic, cotton, rubber, wood, paper, glass, pure water, etc. |
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Combination of Resistances in Series and Parallel |
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Resistors can be combined in different ways. When two or more resistors are connected end to end, so that the same current flows through all of them then, the resistors are said to be in series. |
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Law of Combination of Resistors in Series |
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Let us consider two resistances 'R1' and 'R2' connected in series. A battery of 'V' volts is applied to the ends of this series combination. |
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Law of Combination of Resistance in Parallel |
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Connect two resistors 'R1' and 'R2' in parallel to one another between the points A and B. Connect this combination to a battery of potential 'V'. |
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Heating Effect of Electric Current |
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Energy exists in various forms such as mechanical energy, heat energy, chemical energy, electrical energy, light energy and nuclear energy. According to the law of conservation of energy, energy can be transformed from one form to another. |
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Electric Power |
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The power is the rate of doing work or in other words, it is the work done in one second. |
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Commercial Unit of Electrical Energy |
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Kilowatt - hour is the commercial unit of electrical energy. We have seen that power is the rate of energy consumed or delivered. If 1 joule of energy is used per second, we say that energy is used at the rate of 1 watt. |
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Rating of Electrical Appliances |
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Generally electrical appliances such as an electric bulb, geyser, heater, etc. are rated with power and voltage. If a bulb is rated 100W - 250V, it means that when a bulb is lit on a 250V supply, it consumes 100 W of electric power. This means that, 100 J of electrical energy gets converted into heat and light energy in 1 second. |
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Chemical Effect of Current |
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The fact that chemical changes produce electrical effect was discovered accidentally in 1971, by Luigi Galvani, an Italian professor. He found that an electric current flowed across two dissimilar metals. Volta, professor of natural philosophy successfully reproduced some of Galvani's results using inanimate things. The basic reason for electrochemical effects became clear rather slowly. Scientific investigations in this field actually began with the converse phenomenon namely chemical effects of electrical currents. |
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Magnetic Effect of Electric Current |
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Major progress in understanding magnetism came after the relationship between electricity and magnetism was established by Hans Christian Oersted in 1820. He found that an electric current moves a compass needle and this effect lasts as long as the current flows through the wire. It is then possible to produce magnetism without any magnetic substance at all. |
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Electric Motor |
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An electric motor is a device which converts electrical energy into mechanical energy. |
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Electric Generator (DC) |
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The electric generator is a machine for producing electric current. The electric generator or dynamo converts mechanical energy into electrical energy. |
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Direct Current and Alternating Current |
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If the current flows always in the same direction, it is called 'direct current'. Direction current is represented as DC or dc. The current derived from a cell or a battery is direct current - since it is unidirectional. The positive and negative terminals are fixed. If the current changes direction after equal intervals of time, it is called alternating current. Alternating current can be written as AC or ac. Most of the power stations generate alternating current. The following are the circuit elements representing dc and ac. |
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Domestic Electric Circuit |
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Electric power is usually generated at places which are far from the places where it is consumed. |
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Safety Measures in Electrical Circuits |
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An electric fuse is a device which is used to limit the current in an electric circuit. The use of a fuse is to safeguard the circuit and the appliances connected in the circuit from being damaged. |
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Earthing of an Electric Appliance |
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Usually an electric appliance such as a heater, an iron, etc. are fitted with all the 3 wires namely live, neutral and earth. The earth wire is connected to the metallic body of the appliance. This is done to avoid accidental shock. Suppose due to some defect, the insulation of the live wire inside an electric iron is burnt then the live wire may touch the metallic body of the iron. |
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Summary |
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Electric potential is the condition that determines the flow of charge. Electrical potential at a point in an electric field is defined as the amount of work done in bringing a unit of positive charge from infinity to that point. |
