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Unformatted text preview: , the
circuit in Fig. 3.2(a) is redrawn in Fig. 3.2(b), where we now add i1 , i2 ,
and i3 as the currents through resistors R1 , R2 , and R3 , respectively. At
node 1, applying KCL gives I1 = I2 + i1 + i2 77 The number of nonreference nodes is equal to
the number of independent equations that we
will derive. (a) Figure 3.1 Common symbols for
indicating a reference node. I2 (3.1) At node 2,
I2 + i2 = i3 (c) (b) R2 1 2 (3.2) We now apply Ohm’s law to express the unknown currents i1 , i2 , and i3
in terms of node voltages. The key idea to bear in mind is that, since
resistance is a passive element, by the passive sign convention, current
must always ﬂow from a higher potential to a lower potential. I1 +
v1
− +
v2
− R1 R3 0 (a) Current ﬂows from a higher potential to a lower potential in a resistor. I2 We can express this principle as
i= vhigher − vlower
R v1 i2 R2 i2 v2 i1
(3.3) I1 i3 R1 R3 Note that this principle is in agreement with the way we deﬁned resistance
in Chapter 2 (see...
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 Spring '12
 bkav

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