Introduction to Electric Circuits

Figure 3.13

3A 4fi

Example 3.5

3.6 THEVENIN'S THEOREM

Thevenin, a French engineer, developed work by Helmholtz and published this
theorem in 1883. It may be stated as follows" any linear network containing an
element connected to two terminals A and B may be represented by an
equivalent circuit between those terminals consisting of an emf E0 in series with
a resistor R0.
The emf E0 is the potential difference between the terminals A and B with
the element removed and R0 is the resistance between the terminals A and B
with the element removed and with all sources replaced by their internal
resistances. Ideal voltage sources are replaced by a short circuit and ideal
current sources are replaced by an open circuit.
In any particular problem, of course, we place the two terminals A and B at
either end of the element or part of the circuit in which we wish to determine
the current.

10s 40~

Find the current through the 40 ~ resistor (RE) in the circuit of Fig. 3.14.

A

= 12V

48 DC circuit analysis

Figure 3.14

Solution

9 Step 1: place terminals A and B at either end of the resistor R E.

9 Step 2: represent the circuit by its Thevenin equivalent circuit as shown in

Fig. 3.15.