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Replacing a fuse When a fuse has blown the first step is to turn off the main switch before looking for the cause of the trouble. Sometimes a fuse melts simply because the wire is very old and has become weakened by oxidation, or it can melt from overloading of the circuit. Frequently, fusing is caused by a […]

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Fuses The Electricity Board’s fuse is usually of the cartridge type, in which the fuse element is enclosed in a tubular container filled with quartz sand. The ordinary house fuses generally consist of short lengths of tinned copper wire or cartridge. fuses fitted into carriers made of porcelain or other insulating material. The special fused plug used in ring […]

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Domestic electric installation The cable bringing the mains electricity supply into a house contains two wires, one of which is “live” and the other “neutral”. The neutral wire is earthed at the local transformer substation, so it is at earth potential. At some convenient place inside the house the service cable enters a sealed box, where the live […]

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Board of Trade unit of electric energy. The kilowatt hour If an electricity meter is inspected it will be found to have the abbreviation kWh inscribed on it. This stands for kilowatt hour, which is the commercial unit of electric energy. As its name implies, the kilowatt hour is the energy supplied by a rate of working of 1000 […]

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Calculation of the work done by an electric current From the definition of the volt (page 405), it follows that if a p.d. of 1 volt is applied o the ends of a conductor and I coulomb of electricity passes through it the work one is I joule. Hence if the p.d. applied is V in volts and […]

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Electric power If a piece of electrical equipment is examined it will usually be found to have a label or engraved plate giving the working voltage and the power consumption in watts. For example, an electric lamp may be marked 240 V 60 W, or a fire 240 V 3 kW. The abbreviation kW stands for kilowatt (1 […]

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Energy in an electric circuit Before studying the rest of this chapter the reader should revise definitions, given earlier in the book, of the following quantities: joule, watt, ampere, coulomb, volt, and ohm. When a potential difference is applied to the ends of a conductor some of the electrons inside it are set in motion by the electric […]

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Heating by electricity The heating element in an ordinary radiant electric fire is a length of resistance wire which becomes raised to a temperature of about 900 DC when current is passed through it. The wire is supported on a fireclay rod or bar or coiled inside a fused silica tube. The alloy from which the wire is […]

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Fluorescent lighting Besides giving out coloured light, a mercury vapour discharge tube also emits ultraviolet light. When ultraviolet light, which is itself invisible, falls on certain minerals they glow brilliantly with various colours. This phenomenon is called fluorescence. Accordingly, the inside of a mercury discharge tube may be coated with a mixture of various powders which give out either […]

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Discharge lamps If some gas at low pressure is contained in a tube fitted with metal electrodes at each end the gas glows with a characteristic colour when a high voltage is applied to the electrodes. The electric field set up inside the tube causes ions present in the gas to move with high speeds. As a result […]