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

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

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

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

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

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

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

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

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