Where, the equivalent resistance,
R
eq
, is the sum of three resister in figure 25 which is called
equivalent resistance. In general, if there are
N
resisters in series, their equivalent resistance
is equal
to the sum of all resistance, namely:
R
eq
=
∑
i=1
N
R
i
Figure 26. A
parallel circuit
Two or more resisters are said to be parallel if the same voltage is across each of resisters.
Consider the three parallel resisters as illustrated in figure 26, a equivalent circuit for figure 26
is derived through Kirchoff’s
Current Law as
−
I +
V
s
R
1
+
V
s
R
2
+
V
s
R
3
=0
Above equivalent resistance can be also rewritten as:
R
eq
=
V
s
I =
1
1
R
1
+
1
R
2
+
1
R
3
In general, if there are
N
resisters
in parallel,
R
eq
=
V
s
I =
1
1
R
1
+
1
R
2
+ ⋯ +
1
R
N
Advances
in Bioengineering
208
