Dave MW Posted June 16, 2012 Share Posted June 16, 2012 Help - I know this is a schoolboy question, but I have just bought a few bits and peices from Maplins to show my 6 year old the basics of a circuit. A simple 6 volt battery pack, wire, switch and a 6v .1 amp bulb in a holder. I used a multimeter to test the circuit which showed .1 amp current, 6.35 volts and 8.3 ohms resistance - Ohms Law would suggest that the resistance should have read 63.5 ohms. I don't know who is more confused - my son or me. Can anyone help? Link to comment Share on other sites More sharing options...
John Cuthber Posted June 16, 2012 Share Posted June 16, 2012 Well, it seems you have both learned something. The resistance of a piece of wire varies with temperature. For pure metals the resistance rises roughly with the absolute temperature. The tungsten filament in the bulb when it is lit up is very hot indeed and so it's resistance is much higher than when it's cold. Link to comment Share on other sites More sharing options...
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