1. Review Lecture 2

2. Copyright © 2009 Pearson Education, Inc. Admin: Mid-term is in class on Wednesday. No assignment this week. Labs and discussion sessions run as usual Extra Office hours 2-4pm Monday: Dr Holder Sharp Lab 222 2-4pm Tuesday: Dr Holder Sharp Lab 222 Email is also OK (but visits work better)

3. Copyright © 2009 Pearson Education, Inc. What does the test cover? Electric fields and forces. Potential of an infinite plane Field between two plates Capacitors Capacitance Charge and energy on a capacitor Combination rules Capacitors in steady state Inductors Inductance Current and energy in an inductor Combination rules Ch. 21-5, -6, -7, -8 Ch. 24-1, -2, -3, -4 Ch. 30-2, -3

4. Copyright © 2009 Pearson Education, Inc. What does the test cover? AC circuits AC waves RMS quantities Complex representation (including phasors) Components in AC circuits Resistors Capacitors (Reactance, impedance, i-v relation) Inductors (Reactance, impedance, i-v relation) AC circuit analysis Transient circuits Capacitor charging and discharging (RC circuits) Inductor charging and discharging (LR circuits) LC circuits – Oscillators LRC circuits – Damped Oscillators Filters Ch. 26-5 Ch. 30-4 Ch. 30-5 Ch. 30-6

5. Copyright © 2009 Pearson Education, Inc. What formulae will I have?

6. Copyright © 2009 Pearson Education, Inc. What will be the format of the exam? Similar to the last mid-term – some short answer, plus a few longer questions Rules Closed book exam – no notes or textbooks. Please seat yourselves with at least one space between you. A scientific calculator is required Graphing calculators are OK – but I can’t give partial credit for the algebra if you don’t show it. No phones/ phone calculators Students with accommodations can use the test center – but fill out the DSS form.

7. Copyright © 2009 Pearson Education, Inc. How should I study? 15% of your grade The best resource is the lecture notes – in particular, make sure you can solve all of the worked examples, without the solutions in front of you. The textbook is also useful. Review the discussion problems, and homework problems. Come to office hours (soon!) if anything is not clear – or drop me an email, but office hours are usually much more effective

8. Copyright © 2009 Pearson Education, Inc. 24-2 Determination of Capacitance Example 24-1: Capacitor calculations. (a)Calculate the capacitance of a parallel-plate capacitor whose plates are 20 cm × 3.0 cm and are separated by a 1.0-mm air gap. (b) What is the charge on each plate if a 12-V battery is connected across the two plates?

9. Copyright © 2009 Pearson Education, Inc. 24-4 Electric Energy Storage Example 24-8: Energy stored in a capacitor. A camera flash unit stores energy in a 150-μF capacitor at 200 V. (a) How much electric energy can be stored? (b) What is the power output if nearly all this energy is released in 1.0 ms?

10. Copyright © 2009 Pearson Education, Inc. 24-4 Electric Energy Storage Conceptual Example 24-9: Capacitor plate separation increased. A parallel-plate capacitor carries charge Q and is then disconnected from a battery. The two plates are initially separated by a distance d. Suppose the plates are pulled apart until the separation is 2d. How has the energy stored in this capacitor changed? Remember that the charge is conserved

11. parallel series Capacitors Inductors parallel series All have the same charge All have the same voltage

12. C1 = 2.0 μF, C2 = 1.5 μF, and C3 = 3.0 μF, what arrangement will give the minimum voltage drop across the 2.0-μF capacitor C1? Minimum voltage drop will be across maximum equivalent capacitance

13. C1 = 2.0 μF, C2 = 1.5 μF, and C3 = 3.0 μF, what arrangement will give the minimum voltage drop across the 2.0-μF capacitor C1? If the battery provides 12V, what is the voltage drop across C1? C 13 =5.0 μF C eq = C 13 C 2 /(C 13 + C 2 )=1.15μF V eq =12V Q=VC=13.8μC Q=13.8μC V 13 =Q/C 13 =2.8V V 13 =V 1 C 13 =5.0 μF

14. Capacitative Impedance Inductive Impedance Resistive Impedance Impedance is the complex form of a component’s resistance Current leads voltage by 90° in a capacitor Current has to flow first, to push charge onto the plates, which creates the voltage Voltage leads current by 90° in an inductor Voltage and current are in phase in a resistor

15. Copyright © 2009 Pearson Education, Inc. What is the rms current in the circuit shown if C = 1.0 μF and V peak = 170 V? Calculate (a) for f = 60 Hz and then (b) for f = 6.0 x 10 5 Hz. Note: we can simply use reactance (X C ) if dealing with phase independent quantities like rms. But the answer is not valid at any given instant in time: for that we need the impedance (Z C ) V rms = V peak /√2 ω = 2πf

16. Current Divider! Sketch the input current and the current through the 1H inductance ω = 2πf f=1/T I L2 = I S (R EQ /R)

17. Copyright © 2009 Pearson Education, Inc. The capacitor is: Charging with the switch in position 1. Discharging with the switch in position 2. a) Will it take longer to charge or discharge? b) What is the current through the resistor at the start of the charging cycle? c) What is the maximum Charge on the capacitor? d) How long will it take to reach half of this maximum charge? Kirchhoff’s loop rule. τ =RC charging

18. Which of the following are high-pass or low-pass filters? Answers: (b) and (c) are high- pass; (a) and (d) are low-pass