**Thevenin’s theorem:** Thervenin’s theorem states that any two terminal, linear, bilateral network can be replaced by an equivalent circuits consisting of a voltage source and series resistor with it. Where equivalent voltage (Vth) is voltage across the open circuited terminal pair and equivalent resistant(Rth) is a resistance seen from open circuited terminal, when all the independent sources are replaced by their internal impedances.

**1. Procedure to calculate Vth:**
**a.** Identify the load and remove from the circuit.
**b.** After getting the open circuited terminal pair, calculate the potential across that by any method of analysis.
**c.** This open circuit voltage is Vth.

**2. Rth calculation:**
**Case I:** Network with no dependent sources:
**a.** Identify the load and remove from the network and get the open circuited terminal.
**b.** Replace all the independent sources by their internal impedances.
**c.** Calculate equivalent resistance across the open circuited terminal by using series/ Parallel/Star/delta simplification, that will be Rth .
**d.** Draw the equivalent circuit.

**Case II: Network consist dependent and independent source together:**
**a.** Identify the load and remove form the circuit.
**b.** Replace all the independent sources by their internal impedances
**c.** Apply a test source of ‘V’ and assume the current is ‘I’ outside from it.
Or
Apply a test source of ‘I’ and assume the voltage is ‘V’ across it
**d.** Calculate ratio V/I . This will be Rth.