Experiment 5: Thevenin’s Theorem

Aim

Verification of Thevenin’s Theorem

Components and Equipment Required

• Multimeter
• Power supply
• Breadboard
• 3 Resistors
• Connecting wires

Theory

Thevenin’s theorem states that a linear two-terminal circuit can be replaced by an equivalent circuit consisting of a voltage source $V_{Th}$ in series with a resistor $R_{Th}$, where $V_{Th}$ is the open-circuit voltage at the terminals and $R_{Th}$ is the input or equivalent resistance at the terminals when the independent sources are turned off.

The basic steps for solving a circuit using Thevenin’s Theorem are as follows: 1. Remove the load resistor $R_L$ or component concerned.
2. Find $R_{Th}$ by shorting all voltage sources or by open-circuiting all the current sources.
3. Find $V_{Th}$ by the usual circuit analysis methods.
4. Find the current flowing through the load resistor $R_L$.

Formulas used:
$$I_L = \frac{V_{TH}}{R_{TH} + R_L}$$

Circuit Diagram

Figure 1: Original Circuit

Figure 2: For $V_{Th}$

Figure 3: For $R_{Th}$

Procedure

1. Connect the circuit as shown in Figure 1.
2. Set the particular voltage value and note down all readings.
3. Connect the circuit as in Figure 2 to obtain the Thevenin voltage. Remove the load resistor from the original circuit and calculate the voltage across the open terminals to find $V_{Th}$.
4. Connect the circuit as in Figure 3 to obtain Thevenin resistance. Remove all power sources (short voltage sources and open current sources) and calculate total resistance between open terminals to find $R_{Th}$.

Observation Table

Result

Thus, the Thevenin’s Theorem is verified.

Precautions

• Keep the circuit neat and clean.
• Ensure the power supply and ammeter are working properly.
• Avoid short circuiting the output terminals.