Kirchhoff ’ s Current Law

Chapter 2.6 Kirchhoff ’ s Current Law

Fundamental Electrical and Electronic Principles Third Edition Book
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Fundamental Electrical and Electronic Principles Third Edition Book

  • 48Fundamental Electrical and Electronic Principles Notice that the p.d. method is an easier and less cumbersomeone than current division when more than two resistors are connected in parallel. (d) P 3 I32 R 3 watt or V BC I 3 watt or VRBC23 watt and using the fi rst of these alternative equation: P 3 2 2 5 P 3 20 W Ans It is left to the reader to confi rm that the other two power equations above yield the same answer. 2.6 Kirchhoff ’ s Current Law We have already put this law into practice, though without stating it explicitly. The law states that the algebraic sum of the currents at any junction of a circuit is zero. Another, and perhaps simpler, way of stating this is to say that the sum of the currents arriving at a junction is equal to the sum of the currents leaving that junction. Thus we have applied the law with parallel circuits, where the assumption has been made that the sum of the branch currents equals the current drawn from the source. Expressing the law in the form of an equation we have: I0 (2.9) where the symbol means ‘ the sum of ’ . Figure 2.16 illustrates a junction within a circuit with a number of currents arriving and leaving the junction. Applying Kirchhoff ’ s current law yields: IIIII123450 where ‘ ’ signs have been used to denote currents arriving and ‘ ’signs for currents leaving the junction. This equation can be transposed to comply with the alternative statement for the law, thus: IIIII13425I2I3I1I4I5 Fig. 2.16