Thevenin's theorem allows you to replace a network with what two elements?

• A. A single voltage source in series with a single resistance
• B. A single current source in parallel with a resistance
• C. A voltage source in parallel with a capacitance
• D. A current source in series with an inductance

Answer: (A)

The essential idea is that any linear network can be replaced from the outside by just a single voltage source in series with a resistor. The voltage source represents the open-circuit voltage the network would deliver to a load, while the series resistor represents the net internal resistance seen from the terminals. With this arrangement, for any load connected across the same two terminals, the current and terminal voltage will match those of the original network because the voltage source and series resistance reproduce the same V–I behavior.

To find these two elements in practice, you determine the open-circuit voltage across the output terminals (this gives the Thevenin voltage) and then with all independent sources deactivated, find the resistance seen from the terminals (this gives the Thevenin resistance). The pair—a voltage source in series with a resistor—is the Thevenin equivalent. (The dual form, a current source in parallel with a resistor, is called the Norton equivalent.)