1. Maximum Power Transfer Theorem:
Statement: Maximum Power Transfer Theorem states that “maximum power is transferred from the source to the load when the load resistance is equal to the Thevenin’s equivalent resistance”.
i.e, RL = RTH

2. Substitute the value of I,
Proof:
and
Substitute the value of I,

3. For max power,

4. Now, maximum power transfer is given by

6. Output power=I2RL
Input power= I2RTh
η = o/p power / (o/p power+i/p power)
=I2RL / I2(RL+RTh)
For max efficiency RL=RTh
Hence efficiency η = RL/(2RL)*100= 50%

7. Example Evaluate RL for maximum power transfer and find the power
Note: To solve a question for maximum power transfer, the thevenin equivalent needs to be calculated.

8. Calculation of Vth and Rth:2 10
Rth 3 2
Vth = VA - VB = 6V
Rth=(2׀׀3)+10+2=13.2Ω

9. Thevenin’s equivalent circuit
RL should be set to 13.2Ω to get max. power transfer
Max. power is

13. Example:
Evaluate RL for maximum power transfer and find the power

14. Calculation of RTH :
RL = RTH =6Ω

15. Calculation of VTH :

17. RL must equal to RTh = 6 ohms
The maximum power transferred=