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Brock University Physics 1P22/1P92 Winter 2015 Dr. D’Agostino Reading Guide for Ch. 20, Electric Circuits My lecture notes discuss analogies (models, if you wish) that are not discussed in the textbook, but which my students in previous runnings of this course have found helpful in understanding electric current. I’ll discuss them in class, and you can find explanations in my lecture notes: the “necklace” analogy the “money” analogy the “playground” analogy the “water pressure” analogy And remember that the simplified model of electric current that is presented in the first few pages of the lecture notes is itself an analogy! Also make careful note of the symbols used to represent various circuit elements, and practice analyzing circuit diagrams. 1 Electromotive Force and Electric Current What is emf? How does a battery work? (You won’t need to know the fine details, but you should understand what a battery does to electric charge that flows through it. You might find it helpful to think in terms of the “charge escalator” model presented in the lecture notes.) What is the definition of electric current? What is direct current? What is alternating current? What is “conventional current?” 2 Ohm’s Law What is electrical resistance? What is Ohm’s Law? What is a resistor? 3 Resistance and Resistivity What is the resistivity of a material? How is the resistance of an object connected to the resistivity of the material that the object is made of? What is the temperature coefficient of resistivity? What is superconductivity? 1 4 Electric Power How can you calculate the power dissipated in an electric circuit element? How can you calculate the energy converted (“consumed”) by an electric circuit element? How can you calculate the cost of energy converted (“consumed”) by an electric circuit element? 5 Alternating Current What is alternating current? How do the voltage and current vary in alternating current? What is an rms quantity? What is the relation between an rms quantity and the peak value of the quantity? What is the relation between the average power dissipation over a cycle and corresponding peak and rms quantities? 6 Series Wiring What is a series circuit? What does it mean for two circuit elements to be connected in series? What is equivalent resistance? What is the equivalent resistance for a number of resistors connected in series? How is the power dissipated by a series circuit related to the power dissipated in each circuit element? 7 Parallel Wiring What is a parallel circuit? What does it mean for two circuit elements to be connected in parallel? What is the equivalent resistance for a number of resistors connected in parallel? How is the power dissipated by a parallel circuit related to the power dissipated in each circuit element? Why are home electrical systems wired in parallel, not series? 8 Circuits Wired Partly in Series and Partly in Parallel What is the “ideal wire” model? (This may not be explained directly in the textbook, but see the lecture notes.) Practice analyzing simple and complex circuits. 2 9 Internal Resistance OMIT this section; it discusses details of batteries that go beyond the scope of this course. 10 Kirchhoff ’s Rules Kirchhoff’s rules are also called Kirchhoff’s laws; both terms are in common use. What is the law of conservation of current? What is Kirchhoff’s junction law? How is Kirchhoff’s junction law connected to the law of conservation of current? What is Kirchhoff’s loop law? How is Kirchhoff’s loop law connected to the law of conservation of energy? 11 The Measurement of Current and Voltage OMIT this section; it discusses details of measurement that go beyond the scope of this course. 12 Capacitors in Series and Parallel What is the equivalent capacitance for a number of capacitors connected in series? What is the equivalent capacitance for a number of capacitors connected in parallel? 13 RC circuits What is an RC circuit? How do RC circuits behave? What are some applications of RC circuits? 14 Safety and Physiological Effects of Current What is a short circuit? Why is a short circuit dangerous? What is electrical grounding? What is its purpose? What are some physiological effects of electrical current? What are typical dangerous levels of electrical current and voltage? What are some principles you can use to maintain safety around electrical equipment in the home? 3