Download 19-2 EMF and Terminal Voltage

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=e-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… DV=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