Chapter 26 Direct-Current Circuits

1
Chapter 26 Direct-Current Circuits

• Study resistors in series and parallel
• Consider Kirchoffs Rules
• The design and use of electronic measuring
  instruments
• R-C circuits
• The applications of circuits in household wiring

2
Resistors in Series and Parallel
Resistors in Series
Figure 26-1
Resistors in Parallel
Figure 26-1
3
Series and parallel combination resistors

• Consider Problem-Solving Strategy 26.1.
• Follow Example 26.1 guided by Figure 26.3 below.
• Follow Example 26.2.

4
Kirchoffs Rules Ijunctions

• The algebraic sum of the currents into any
  junction is zero.

5
Kirchhoffs Laws
Kirchhoffs Current Law
Proof
Charge cant build up at the junction.
Figure 26-7
Kirchhoffs Current Law - Example
Figure 26-8
6
Kirchoffs Rules IIloops

• The algebraic sum of the potential differences in
  any loop, including those associated with emfs
  and those of resistive elements, must equal zero.

7
Kirchhoffs Voltage Law Two Loop Example
Loop 1
Loop 1
Loop 2
Loop 2
8
Kirchhoffs Laws - A Single Loop Circuit
Example 26-3
a) Solve for I b) Solve for Vab c) Solve for
power output of the emf of each battery
Figure 26-10
9
Kirchoffs Rules IIIexamples and strategy

• Read through Problem-Solving Strategy 26.2.
  Figure 26.9 illustrates this strategy.
• Refer to Example 26.3, illustrated by Figure
  26.10.

10
Kirchoffs Rules IVexamples

• Refer to Example 26.4, illustrated by Figure
  26.11.
• Consider Example 26.5.
• Refer to Example 26.6, illustrated by Figure
  26.12.
• Review Example 26.7.

11
R-C Circuits (Chapter 26, Sec 4)
Charging a Capacitor
0.37 I0
0.63 Qf
Time Constant
Figure 26-20
Figure 26-21
(26-14)
12
R-C Circuits (Chapter 26, Sec 4)
Discharging a Capacitor
Time Constant
(26-14)
Figure 26-23
Figure 26-22
13
DArsonvals galvanometer

• Well call it simply meter henceforth.
• The meter is a coil of wire mounted next to a
  permanent magnet. Any current passing through the
  coil will induce magnetism in the coil. The
  interaction of the new electromagnetism and the
  permanent magnet will move the meter indicator
  mounted to the coil.

14
The Ammeter and Voltmeter

• The ammeter (sometimes prefixed with milli or
  micro because the currents to be measured are
  routinely thousandths or millionths of an ampere)
  may be used to measure current OR voltage. A
  shunt resistor makes this conversion as shown
  below in Figure 26.15.
• Consider Example 26.8 to follow a current
  example. Consider Example 26.9 to follow a
  voltage example.

15
Ammeter Design
Vab Vab Ifs Rc (Ia Ifs) Rsh
Ifs 1 mA Rc 50 ohm Ia 50 mA Rsh ?
16
Voltmeter Design
Vab Ifs (Rc Rs ) Solve for Rs Rs (Vab -
Ifs Rc)/ Ifs
Ifs 1 mA Rc 20 ohm Vab 10 v Rs ?
17
Ohmmeters and digital multimeters

• An ohmmeter is designed specifically to measure
  resistance.
• Refer to Figure 26.17 and Figure 26.18 below to
  see an ohmmeter wiring diagram and a photograph
  of a digital multimeter. The multimeter can
  measure current, voltage, or resistance over a
  wide range.

18
Power Distribution Systems
240-V line black, red Neutral
Black
White
120 v
One phase of the 240-V line
We buy energy from the Power Company, not
power kW x time watt-seconds Joules 1 kWh
(1000W) (3600 s ) 3.6 x 106 W-s 3.6 x 106 J
19
Fuses, circuit breakers, and GFI

• A fuse will melt and a breaker will open the
  circuit if maximum current is reached. See Figure
  26.26.
• GFI stops further current flow when a sudden drop
  in resistance indicates that someone has offered
  a new path to ground. I dont know if it will
  save this worker we see in Figure 26.27 who
  didnt use a grounded drill.

20
The wiring diagram for a typical kitchen

• Consider Figure 26.28 below.
• Follow Example 26.14.

21
Average Retail Price of Electricity cents per
kilowatt-hour
  Residential Residential Commercial1 Commercial1 Industrial1 Industrial1
Census Division Residential Residential Commercial1 Commercial1 Industrial1 Industrial1
and State Residential Residential Commercial1 Commercial1 Industrial1 Industrial1
  Nov-07 Nov-06 Nov-07 Nov-06 Nov-07 Nov-06
New England 16.18 15.58 14.19 13.78 12.75 11.44
Connecticut 18.33 16.92 14.91 14.24 12.46 12.08
Maine 15.42 14.06 13.04 11.91 12.12 9.45
Massachusetts 15.69 15.74 14.38 14.22 14.01 12.53
New Hampshire 14.8 14.22 13.26 13.28 12.32 10.78
Rhode Island 14.62 14.34 13.2 12.81 12.18 12.28
Vermont 14.35 13.57 12.36 11.84 8.79 8.31
U.S. Total 10.69 10.18 9.6 9.24 6.22 6.04