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www.GOALias.blogspot.comFig. 14.15 Fuses used in electrical appliancesFig. 14.14 Fuse used in buildingsthe nichrome wire, tie a thin strand ofsteel wool. (The steel wool is commonlyused for cleaning utensils and isavailable in grocery shops.) If there areany fans in the room, switch them off.Now pass the current through the circuitfor sometime. Observe the strand of steelwool carefully. Note what happens. Doesthe strand of steel wool melt and break?Wires made from some specialmaterials melt quickly and break whenlarge electric currents are passedthrough them. These wires are used formaking electric fuses (Fig.14.14). In allbuildings fuses are inserted in allelectrical circuits. There is a maximumlimit on the current which can safelyflow through a circuit. If by accident thecurrent exceeds this safe limit, the wiresmay become overheated and may causefire. If a proper fuse is there in the circuit,it will blow off and break the circuit. Afuse is thus a safety device whichprevents damages to electrical circuitsand possible fires.Fuses of different kinds are usedfor different purposes. Fig. 14.14 showsfuses used in our houses. Fusesshown in Fig. 14.15 are generally usedin electrical appliances.CAUTIONNever try to investigate an electric fuseconnected to mains circuit on yourown. You may, however, visit anelectric repair shop and compare theburnt out fuses with the new ones.One reason for excessive currents inelectrical circuits is the directtouching of wires. This may happen ifthe insulation on the wires has comeoff due to wear and tear. This maycause a short circuit. Another reasonfor excessive current can be theconnection of many devices to a singlesocket. This may cause overload inthe circuit. You might have readreports in newspapers about firescaused by short circuits andoverloads.We observed the heating effect of theelectric current and learnt how we useit to our advantage. Does the electriccurrent have other effects also?166SCIENCE