In this article, we will discuss the **different methods of finding Thevenin’s resistance (R _{TH})**.

# Case 1: For circuits containing independent sources only

When an electric circuit contains independent sources only,
then the most common method of determining Thevenin’s resistance (R_{TH})
is explained as follows:

**Step I** – Remove
the load resistance.

**Step II** –
Deactivate all the independent current and voltage sources in the circuit by
their internal resistances. For an independent current source, deactivate it by
removing the current generator. For an independent voltage source, deactivate it
by short-circuiting the voltage generator.

**Step III** –
Determine the internal resistance of the network by looking through the open-circuited
load terminals. This will be Thevenin’s resistance (R_{TH}) of the
circuit.

# Case 2: For circuits containing dependent sources or/and independent sources

When a circuit contains dependent sources in addition to or
in absence of the independent source. Then, Thevenin’s resistance (R_{TH})
can be determined by using any of these two following methods.

## First Method: Short-Circuit Method

**Step I** – Remove
the load resistance.

**Step II** – Find
the voltage V_{oc} across the open-circuited load terminals by using
any conventional network solution method.

**Step III** – Now,
short-circuit the load terminals and determine the short-circuit current I_{sc}
flowing through the shorted path.

**Step IV** – Then,
the internal resistance or Thevenin’s resistance R_{TH} of the network
will be,

## Second Method: Test Voltage Method

**Step
I** – Remove the load resistance.

**Step
II** – Deactivate all the independent current and voltage sources.

**Step
III** – Apply a DC test voltage V_{t}
at the open-circuited load terminals.

**Step
IV** – Due to the applied voltage V_{t}, a direct current I_{t}
will flow in the circuit from the load terminals.

**Step
V** – Then, the internal resistance or Thevenin’s resistance R_{TH}
of the circuit will be,

Hence, using any of these above methods,
we can find the internal resistance or Thevenin’s resistance of a given
electric circuit.