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I understand that if there’s low resistance, Ohm’s law shows that the current drawn will be very high. However, isn’t resistance what causes heat in a wire? I get there’s a lot of current going through the wire in a short, and there’s lots of power, but since there’s low resistance how does the energy get transformed into heat? How does a spark or fire start?

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  • $\begingroup$ Joules can be written as $P=V^2/R$, so the lower the resistance the higher the power dissipated. If the material can't dissipate the heat, it will get very hot and can burn. $\endgroup$ – jinawee Nov 1 '15 at 11:06
  • $\begingroup$ you are wrong to say lower resistance means high power dissipation. connecting wires have negligible resistance but still power dissipation is very low. $\endgroup$ – Anubhav Goel Nov 1 '15 at 11:38
  • $\begingroup$ @jinawee What causes the energy of the current to be transformed into thermal energy within the wire, though? I get that heat is not dissipated to the surroundings, but what’s the mechanism for the transformation to thermal energy of the circuit’s electrical energy? $\endgroup$ – lightweaver Nov 1 '15 at 11:54
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power dissipated is more correctly given by H = I^2 RT. a normal wire or gadget has nearly constant resistance. Before short circuit, a little amount of current flows through it which gives minimal power consumption. But during short circuit suddenly large amount of current flows through it for same resistance. So, power dissipated increases too much that it cause fire.

In our normal home circuit we have high resistance in series, in form of inductors and capacitor which does consume negligible energy and almost do not dissipate heat.High resistance means less current. so, like this our device which has normal resistance gets minimal current and work properly. During short circuit let if an inductor is not there , then large current flows through our gadget for its same normal resistance and it burns out.

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