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Q & A: limits of Kirchoff's law

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Most recent answer: 03/17/2013
Q:
How the Kirchoff's Current Law(KCL),is appropriate, i,e; the alzebraic sum of currents in a closed loop is zero, or in other words currents entering into a node is equals to sum of currents leaving that node,this is possible only in case of ideal conductors,where as they does not exist in reality,all the conductors we are using in the circuits must have some internal resistance and some other properties,so it has to offer some losses,then how the input current to a node will equal to currents leaving from that node ?
- Raja Reddy (age 21)
Hyderabad
A:
Kirchoff's law is an excellent approximation because if it were violated electrical charge would be building up in the regions where the incoming and outgoing currents were out of balance. An accumulation of much charge has enormous energy, so that can't go on for long. In a capacitor, charge can flow into one side, but if you look at both sides of the capacitor as a whole the net charge balances. Thus Kirchoff's law applies to the capacitor as a whole.

The sort of losses you talk about are losses of energy. The work done driving a current largely gets lost as heat generated in imperfect conductors. Even as that energy is dribbling away, however, the charge keeps flowing following Kirchoff's law.

Mike W.

(published on 03/17/2013)

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