Chapter 1 Basic DC Circuits

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1

Chapter 1

Basic DC Circuits

2

Objectives


Distinguish between dc and ac and
discuss some of the basic properties of
each.


State and describe the basic circuit
variables including charge, voltage,
current, power, and energy.


Define resistance and conductance and
show the schematic symbol.

3

Objectives


State the properties of the ideal voltage
source and ideal current source models
and show their schematic symbols.


State and apply Ohm’s law.


Discuss voltage and current
measurements and how they are made.


State and apply Kirchoff’s voltage law.


State and apply Kirchoff’s current law.

4

Objectives


Determine equivalent resistance using
series and parallel combinations.


Analyze a single
-
loop (series) circuit to
determine all the variables.


Analyze a single node
-
pair (parallel) circuit
to determine all the variables.


State and apply the voltage divider rule.


State and apply the current divider rule.

5

1
-
1 DC Circuit Variables


Resistance “
R”

(Ohm:

)


Voltage
“V”

(Volt: V)


Current
“I”

(Ampere: A)


Power
“P”

(Watt: W)


Energy
“W”
or
“E”

(Joules: J, or watt
-
hour)

6

Comparison of a DC Voltage and an AC
Voltage

7

Conventional Current Flow in Opposite
Direction to Electron Flow

8

Voltage Between Two Points in a Circuit

9

Schematic Symbols for an Ideal Voltage
Source and a Battery

10

Schematic Symbol for an Ideal Current
Source

11

Schematic Symbol for a Resistance

12

Illustration of a Short Circuit and an Open
Circuit

13

1
-
2 A Very Simple DC Circuit

14

Different Types of Ground

15

Simple Circuit Redrawn with Ground
Symbols

16

1
-
3 Measuring DC Circuit Variables


Ohmmeter


Voltmeter


Ammeter


Wattmeter



Multi
-
meter

17

A Voltmeter is Connected Between Two
Points in a Circuit Across Which the
Voltage is to be Measured

18

An Ammeter is Connected Within the
Branch for Which Current is to be
Measured

19

1
-
4 Power and Energy


Energy:

work performed,
or
capacity to
perform work



Power:

rate of change of energy


20

Reference Directions for Power Delivered

21

Reference Directions for Power Absorbed

1
-
5 Kirchoff’s Laws

22


Kirchoff’s

Voltage Law:
algebraic sum of all
voltages around a closed loop = zero




Kirchoff’s

Current Law:
algebraic sum of all
currents into a node = zero


23

A Loop Used to Illustrate Kirchoff’s
Voltage Law

24

Illustration of Kirchoff’s Current Law at a
Node

25

Circuit of Example 1
-
8

26

Circuit of Example 1
-
9

27

1
-
6 Equivalent Resistance


Series connected resistors


Resistances add


Equivalent resistance greater than largest
resistor


Parallel connected resistors


Conductances

add


Equivalent resistance less than smallest
resistor


Series and parallel combinations

28

Resistances in Series and the Equivalent
Single Resistance

29

Resistances in Parallel and the
Equivalent Single Resistance

30

Circuit of Example 1
-
10

31

Reduction of the Circuit of Example 1
-
10

32

1
-
7 Single
-
Loop or Series Circuit


One current (shared by all circuit’s
components)


Multiple voltages:


Voltage drop (across resistance)


Voltage rise (across sources)


Obey
Kirchoff’s

Voltage Law


Series circuit:
Voltage Divider Rule

33

Representative Single
-
Loop (Series)
Circuit

34

Circuit of Example 1
-
11

35

Circuit of Example 1
-
12

36

1
-
8 Single Node
-
Pair or Parallel Circuit


One voltage (drop or rise) shared by all
circuit’s components


Multiple currents:


Branch currents


Obey
Kirchoff’s

Current Law


Parallel circuit:
Current Divider Rule

37

Single Node
-
Pair (Parallel) Circuit

38

Representative Parallel Circuit with
Current Sources

39

Circuit of Example 1
-
13

40

Circuit of Example 1
-
14

41

1
-
9 Voltage and Current Divider Rules


VDR


V
x

= V
T

* R
x

/ R
T



IDR


I
x

= I
T

* R
T

/ R
x

42

Circuit Used to Illustrate the Voltage
Divider Rule

43

Circuit Used to Illustrate the Current
Divider Rule

44

Circuit of Example 1
-
15

45

Circuit of Example 1
-
16