Page 17 - Basics of Electrical, Electronic and Communication

18 Chapter 2. Kirchoff’s laws

which starting and end points for tracing the path are, in effect,
the same node and touches no other node more than once.

Mesh A mesh is a special case of loop that does not have any other
loops within it or in its interior. All meshes are loops but all
loops are not meshes.

2.1.1 Kirchoff’s Current Law (KCL)

KCL states that at any instant of time, the algebraic sum of currents at
a node is zero.
Mathematically,
N
X
i n = 0
n=1
where N is the number of branches that are connected to the node.
The term ’algebraic sum’ indicates that we have to take account of
the current direction, as well as magnitude, when applying Kirchoff’s
Current Law. Consider the node shown in figure 2.1. By adopting the
sign convention that current flowing into a node is taken as positive
(+) while current flowing out of the node is negative (-), application of
KCL gives

i2
i1

i3
i4

Figure 2.1: KCL

+i 1 + i 2 − i 3 − i 4 = 0

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