Direct Current and Transient Analysis 113
R.2.54 The equivalent resistance Req of a set of two resistors R 1 and R 2 connected in series,
as illustrated in Figure 2.7, is given by its sum.
If n resistors are connected in series (n > 2) denoted by R 1 , R 2 , R 3 , ..., Rn, then the
equivalent resistance Req is given by
RRi
i
n
eq
1
∑
R.2.55 The equivalent resistance Req of two resistors R 1 and R 2 connected in parallel is
given by
R
RR
eq RR
12
12
*
and for the case of the three resistors, the equivalent resistance is given by
R
RRR
eq RR RR RR
123
12 23 31
**
***
For the case of n (n > 3) resistors (R 1 , R 2 , R 3 , ..., Rn) connected in parallel, the equiva-
lent resistance is given by
111 1
RRReq 12 Rn
1
Req
1
i 1 Ri
n
∑
or
R
i Ri
eq n
1
1
∑ 1
FIGURE 2.7
Series equivalent resistor.
R 1
R 2
Req = R 1 + R 2
~~