1. Electric Circuits I: EE 282
Dr. Tewodros A. Zewde

2. : WICHITA STATE UNIVERSITY
EE 282: Circuits I AC Analysis
12/4/2018
Dr. Tewodros A. Zewde

3. Impedance combination
Review
Impedance combination
12/4/2018
Dr. Tewodros A. Zewde

4. Review
12/4/2018
Dr. Tewodros A. Zewde

5. Keep in mind that the two equivalent circuits are related as
Review
Thevenin’s and Norton’s theorems are applied to ac circuits in the same way as they are to dc circuits. The only additional effort arises from the need to manipulate complex numbers.
Keep in mind that the two equivalent circuits are related as
where Vth is the open-circuit voltage while IN is the short- circuit current.
12/4/2018
Dr. Tewodros A. Zewde

6. Exercise
Find the Thevenin equivalent at terminals a-b of the circuit in the following figure.
Find the Norton equivalent of the following circuit as seen from terminals a-b. Use the equivalent to find I0.
12/4/2018
Dr. Tewodros A. Zewde

7. Instantaneous and Average Power
The instantaneous power (in watts) is the power at any instant of time.
Consider the general case of instantaneous power absorbed
The instantaneous power absorbed by the circuit is
12/4/2018
Dr. Tewodros A. Zewde

8. This shows us that the instantaneous power has two parts, i. e
This shows us that the instantaneous power has two parts, i.e., constant or time independent part, and a sinusoidal function whose frequency is twice the angular frequency of the voltage or current.
The instantaneous power changes with time and is therefore difficult to measure. The average power is more convenient to measure. Thus, the average power is given by
or using phasors,
A resistive load ( R ) absorbs power at all times, while a reactive load ( L or C ) absorbs zero average power.
12/4/2018
Dr. Tewodros A. Zewde

9. Exercise
In the first circuit, calculate the average power absorbed by the resistor and inductor. Find the average power supplied by the voltage source.
Calculate the average power absorbed by each of the five elements in the second circuit.
12/4/2018
Dr. Tewodros A. Zewde