Question
Determine the equivalent resistance of networks shown in the figures (a) and (b) below.

Solution
a) Equivalent resistance of network in fig. (a)
The given network is a series combination of four identical units.
Let us consider one such unit as shown in fig. One such unit is equivalent to a parallel combination of 2 Ω and 4 Ω.
Its equivalent resistance is
So, one unit of the given electrical network is a series combination of four resistors, each equal to .
Thus, the combined resistance is 4
=
b) Equivalent resistance of network in fig (b)
Suppose a battery is connected between A and B. Same current will flow through all the resistors. So, all the resistors are connected in series.
∴ Equivalent resistance,
Rs = R + R + R + R + R = 5R
The given network is a series combination of four identical units.
Let us consider one such unit as shown in fig. One such unit is equivalent to a parallel combination of 2 Ω and 4 Ω.
Its equivalent resistance is
So, one unit of the given electrical network is a series combination of four resistors, each equal to .
Thus, the combined resistance is 4
=
b) Equivalent resistance of network in fig (b)
Suppose a battery is connected between A and B. Same current will flow through all the resistors. So, all the resistors are connected in series.
∴ Equivalent resistance,
Rs = R + R + R + R + R = 5R