Increase Decrease Stay the same Sounds complicated – we should calculate it

1. Consider the following circuit, initially with five equal resistance light bulbs. If bulb 2 is replaced with a bulb of lower resistance, what will happen to the brightness of bulb 1? • Increase • Decrease • Stay the same • Sounds complicated – we should calculate it Oregon State University PH 213, Class #18

2. Which of these diagrams represent the same circuit? • a and b • b and c • a and c • a, b, and d • a, b, and c Oregon State University PH 213, Class #18

3. A discharging RC circuit Charge on capacitor: Q = CDVC Current flowing from capacitor: I = –dQ/dt Kirchhoff’s loop rule: DVC – IR = 0 Q/C – IR = 0 Q/C + RdQ/dt = 0 Q = –RC(dQ/dt) Q(t) = Q0e–t/(RC) Exponential decay! So.. I(t) = ?DVC (t) = ? Oregon State University PH 213, Class #18

4. A discharging RC circuit Oregon State University PH 213, Class #18

5. What value resistor will discharge a 1.0 μF capacitor to 10% of its initial charge in 2.0 ms? Oregon State University PH 213, Class #18

6. A charging RC circuit Battery, R, and C; current starts from I = 0 at time t = 0. Q = CDVC on a capacitor, current I = dQ/dt Kirchhoff’s loop rule: DVb – Q/C – IR = 0 DVb – Q/C – (dQ/dt)R = 0 Qmax/C – Q/C – (dQ/dt)R = 0 Q = Qmax(1 – e–t/(RC)), where Qmax = CDVb So.. I(t) = ?DVC (t) = ? Oregon State University PH 213, Class #18

7. A charging RC circuit Oregon State University PH 213, Class #18

8. The switch has been closed for a very long time. Before the switch is opened, what is the current through the 10 Ω resistor? • maximum • positive • zero • Sounds complicated – we should calculate it Oregon State University PH 213, Class #18

9. The switch has been closed for a very long time. At t = 0 s the switch is opened. Immediately after the switch opens, what is the current through the 10 Ω resistor? • maximum • positive • zero • Sounds complicated – we should calculate it Oregon State University PH 213, Class #18

10. Oregon State University PH 213, Class #18