19-2 EMF and Terminal Voltage

•A battery or generator, or other electrical energy creation device, is called the seat or source of electromotive force, emf.

•Batteries have internal resistance.

•Terminal voltage Vab=-Ir•See Example 19-7 Analyzing a circuit.

19-3 Kirchhoff’s Rules

• Kirchhoff’s 1st or junction rule is that at any junction point, the sum of all currents entering the junction must equal the currents leaving the junction.

• Kirchhoff’s 2nd rule or loop rule is that the sum of the changes in potential around any closed path of a circuit must be zero.

19-3 Kirchhoff’s Rules

• Between the two ends of a resistor, the voltage drops… V=IR… and the sign is negative to show the drop…see p 565 Figure 19-12.

19-4 Solving Problems with Kirchhoff’s Rules

• Designate the current flow in each part of the circuit with a subscript. I1, I2, …etc.

• See Example 19-8 Using Kirchhoff’s rules.

• See p 566 and p567

19-5 EMFs in Series and Parallel

• When 2 or more EMFs are placed in series, the algebraic sum of their potentials is the total potential for the circuit.

• Remember their internal resistance is a factor.

• Series with + to+ and – to – are used for charging and the sum is up then down…

• See p 568 a,b,c

19-5 EMFs in Series and Parallel

• EMFs placed in parallel maintian the same voltage, but provide more current.

HOMEWORK

• P582 18-21,24-28 due Monday BOP