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Chapter 2-3
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
1
T. Elsarnagawy, mde207, 311
2
Chapter 2-3
Electrical symbols
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
Chapter 2-3
3
Basic circuit measurements
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
4
Chapter 2-3
Meter symbols
Digital
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
Bar graph
Analog
T. Elsarnagawy, mde207, 311
5
Chapter 2-3
Current measurement
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
Chapter 2-3
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
6
T. Elsarnagawy, mde207, 311
7
Chapter 2-3
Current measurement
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
8
Chapter 2-3
Current measurement
Ammeter connection (series)
+
-
!!Polarity a shown
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
9
Chapter 2-3
Voltage measurement
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
Chapter 2-3
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
10
T. Elsarnagawy, mde207, 311
11
Chapter 2-3
Voltage measurement
Voltmeter across the component (parallel)
+ve to +ve
-ve to -ve
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
Chapter 2-3
12
Resistance measurement
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
Chapter 2-3
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
13
T. Elsarnagawy, mde207, 311
Chapter 2-3
14
Resistance measurement
Disconnect R then make the measurement
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
15
Chapter 2-3
Safety note
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
16
Chapter 2-3
Physical effects of electrical current
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
17
Chapter 2-3
Ohm’s Law
V-I-R
Principles of Electric Circuits, Conventional Flow,
9th ed., Floyd
T. Elsarnagawy, mde207, 311
18
Chapter 2-3
Review of V, I, and R
Voltage is the amount of energy per charge available to
move electrons from one point to another in a circuit.
Current is the rate of charge flow and is measured in
amperes.
Resistance is the opposition to current and is measured
in ohms.
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
19
Chapter 2-3
The most important fundamental law in electronics is
Ohm’s law, which relates voltage, current, and resistance.
Georg Simon Ohm (1787-1854) studied the relationship
between voltage, current, and resistance and formulated
the equation that bears his name. In terms of current,
Ohm’s law states
V
I
R
What is the current from a 12 V source if the
resistance is 10 W? 1.2 A
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
20
Chapter 2-3
Ohm’s law
If you need to solve for voltage, Ohm’s law is:
V  IR
What is the voltage across a 680 W resistor if the
current is 26.5 mA? 18 V
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
21
Chapter 2-3
Ohm’s law
V
If you need to solve for resistance, Ohm’s law is: R 
I
What is the (hot)
resistance of the bulb? 138 W
OFF
V
Hz
V
120 V
mV
A
Range
Autorange
Touc h/Hold
1s
1s
10 A
V
40 mA
COM
Fused
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
22
Chapter 2-3
A student takes data for a resistor and fits the straight
ofthe
Current
versus
Voltage
lineGraph
shown to
data. What
is the
resistance and the
conductance of the resistor?
16
The slope represents the
conductance.
14.8 mA - 0 mA
 1.48 mS
10.0 V - 0 V
The reciprocal of the
conductance is the
resistance:
R 
I (mA)
G
14
12
8
4
1
1

 676 Ω
G 1.48 mS
0
V
R
I
0
2
4
6
8
10
V (V)
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
23
Chapter 2-3
Graph of Current versus Voltage
10
8.0
Current (mA)
Notice that the plot of
current versus voltage for a
fixed resistor is a line with
a positive slope. What is
the resistance indicated by
the graph?
2.7 kW
6.0
4.0
2.0
What is its
conductance? 0.37 mS
0
0
10
20
30
Voltage (V)
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
24
Chapter 2-3
Graph of Current versus Resistance
V  IR
?
10
8.0
Current (mA)
If resistance is varied
for a constant voltage,
the current - resistance
curve plots a hyperbola.
6.0
4.0
2.0
0
0
What is the curve for
a 3 V source?
1.0
2.0
3.0
Resistance (kW )
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
25
Chapter 2-3
Application of Ohm’s law
26.8 mA
+
m
DC Am
eter -
Power Supply
V
A
+15 V
Gnd
5 V 2A
- +
- +
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
Chapter 2-3
26
Selected Key Terms
Linear Characterized by a straight-line relationship.
Ohm’s law A law stating that current is directly
proportional to voltage and inversely
proportional to current.
Troubleshooting A systematic process of isolating, identifying,
and correcting a fault in a circuit or system.
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
27
Chapter 2-3
1. Holding the voltage constant, and plotting the current
against the resistance as resistance is varied will form a
a. straight line with a positive slope
b. straight line with a negative slope
c. parabola
d. hyperbola
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
28
Chapter 2-3
2. When the current is plotted against the voltage for a
fixed resistor, the plot is a
a. straight line with a positive slope
b. straight line with a negative slope
c. parabola
d. hyperbola
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
Chapter 2-3
29
Quiz
3. For constant voltage in a circuit, doubling the resistance
means
a. doubling the current
b. halving the current
c. there is no change in the current
d. depends on the amount of voltage
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
Chapter 2-3
30
Quiz
5. If the current in a 330 W resistor is 15 mA, the applied
voltage is approximately
a. 5.0 V
b. 22 V
c. 46 V
d. 60 V
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
31
Chapter 2-3
Quiz
7. The circuit with the largest current is
a. (a)
b. (b)
c. (c)
d. (d)
+12 V
R
10 kW
+15 V
(a)
R
15 kW
(b)
+18 V
R
22 kW
(c)
+24 V
R
27 kW
(d)
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
32
Chapter 2-3
Quiz
8. The circuit with the smallest current is
a. (a)
b. (b)
c. (c)
d. (d)
+12 V
R
10 kW
+15 V
(a)
R
15 kW
(b)
+18 V
R
22 kW
(c)
+24 V
R
27 kW
(d)
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd
Chapter 2-3
33
Quiz
Answers:
1. d
6. c
2. a
7. a
3. b
8. c
4. b
9. d
5. a
10. c
T.Elsarnagawy, mde207, 311
Principles of Electric Circuits, Conventional Flow, 9th ed.
Floyd