Transcript DC CIRCUITS: Chapter 26 - San Jose State University

DC CIRCUITS: Chapter 26
• Series and parallel resistors
• Kirchhoff’s Rules for network problems
• Electrical meters and household circuits
C 2009 J. F. Becker
DIRECT-CURRENT (DC) CIRCUITS
In this chapter we will study methods of
analyzing more complicated circuits
having several sources, resistors, and
other circuit elements.
In general, we will find the current and
power dissipation in each circuit element.
First we consider ways to simplify
resistors connected in a circuit in series
and parallel.
Second we consider Kirchhoff’s two rules
to simplify more complicated networks.
C 2009 J. F. Becker
Resistors connected in a circuit in series or
parallel can be simplified using the following:
Series connection
Parallel connection
Method of simplifying the circuit in (a) below
to get the equivalent resistance.
We can then calculate the power P = I2 R
dissipated in each resistor.
Ch. 26 #11: Four equivalent light bulbs
R1 = R2 = R3 = R4 = 4.50 W, emf = 9.00 Volts.
Find current and power in each light bulb.
Which bulb is brightest?
Later, if bulb #4 is removed which bulbs get
brighter? Dimmer?
On course website,
see old Test #1 from
semesters S-04, F-03, and others
for typical DC circuit problems,
AND other typical problems on
tests…
C 2009 J. F. Becker
These complex circuits cannot
be reduced to series –
parallel combinations.
So use Kirchhoff’s Rules:
1. S Ij = 0 (junction rule, valid
at any junction);
conservation of charge
2. S (DVj ) = 0 (loop rule, valid
for any closed loop);
conservation of energy
Use Kirchhoff’s junction rule at point “a” to
reduce the number of unknown BRANCH
currents from three to two.
ELECTRICAL MEASURING INSTRUMENTS –
METERS
A d’Arsonval galvanometer meter movement:
AMMETERS have a very small shunt resistor in them
to reduce the effect of introducing the meter
resistance into the circuit being measured.
VOLTMETERS (DV) have a very large series resistor
in them to reduce the amount of current drawn from
the circuit being measured.
House wiring circuits
Hand drill circuit with ground wire for
safety
Note: Section 26.4 Resistance-Capacitance
(RC) Circuits will be deferred until later
Next, back to the second half of Chapter 21:
•Chapter 21 Electric Field and Coulomb’s Law
and Vectors
• Chapter 22 Gauss’s Law
• Chapter 23 Electric Potential
• Chapter 24 Capacitance and Dielectrics
C 2009 J. F. Becker
Review
See www.physics.edu/becker/physics51
C 2009 J. F. Becker