1. 1 Discussion about the mid-term 8. In those hard times, people connected two light bulbs in series to prolong the lifetime of them so as to save money on light bulbs. If a person connects two 40W/220V light bulbs in series to a 220V line, what is the actual power consumed by one light bulb in this configuration? assuming the filament’s resistance does not change much with temperature.

2. 2 Discussion about the mid-term 10. Calculate the power consumed by R1 and the potential at point A.

3. 3 Alternating Current and RLC Circuits Power of RLC in AC circuits  Only the R (resistor) consumes power. The C and L store energy, but do not consume it.  Power consumed by a resistor is P R = RI 2 = RI 2 MAX SIN 2 (ωt+φ) at time t.  Average over one period, one gets the average power consumed of the RLC in an AC circuit with V = V MAX SIN(ωt) P avg = I rms V rms COS(φ) where Z is the impedence φ is the phase angle between the current and voltage. COS(φ) is called the power factor. Discussion: When COS(φ)  0, φ  π/2, P avg  0. almost no power is dissipated through the resistor. When COS(φ)  1, φ  0, Pavg  maximum, the circuit resonates.

4. 4 Alternating Current and RLC Circuits Summary:  RLC circuit:  Current and Voltage:  Impedance and phase angle  Resonant condition and frequency  Power in AC circuit  Average voltage, current and power  Power dissipated of RLC in an AC circuit. I V VLVL VCVC VRVR V V L -V C φ

5. 5 Example problem 1.1

6. 6 Example problem 1.2 A simple loop circuit has an inductor with inductance 4.6×10 −3 H and a capacitor with capacitance 2.8×10 −6 F in series. At a certain time, the current is at its maximum, 5.1 A. (a) What is the charge on the capacitor at this time? (b) What is the maximum charge on the capacitor?

7. 7 Example problem 2

8. 8 Example problem 3

9. 9 Example problem 4