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Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
1
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
2
Electrical symbols
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
3
Basic circuit measurements
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
4
Meter symbols
Digital Bar graph Analog
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
5
Current measurement
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
6
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
7
Current measurement
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
8
Current measurement Ammeter connection (series)
+ -
!!Polarity a shown
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
9
Voltage measurement
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
10
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
11
Voltage measurementVoltmeter across the component (parallel)+ve to +ve-ve to -ve
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
12
Resistance measurement
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
13
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
14
Resistance measurement
Disconnect R then make the measurement
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
15
Safety note
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
16
Physical effects of electrical current
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd
T. Elsarnagawy, mde207, 311
17
Ohm’s Law
V-I-RV-I-R
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
18
Voltage is
Review of V, I, and R
the amount of energy per charge available tomove 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.
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
19
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
VI
R
What is the current from a 12 V source if the resistance is 10 ? 1.2 A
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
20
Ohm’s law
If you need to solve for voltage, Ohm’s law is:
What is the voltage across a 680 resistor if the current is 26.5 mA? 18 V
V IR
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
21
Ohm’s law
If you need to solve for resistance, Ohm’s law is:V
RI
120 V
V
1 s
1 s
40 m A
1 0 A
C O M
Ra ng eAuto ra ng eTo uc h/Ho ld
Fused
O FF V
V
Hz
m V
A
What is the (hot) resistance of the bulb? 138
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
22
Graph of Current versus Voltage
I (m
A)
V (V )
00
2 4
4
6 8
8
10
12
14
16
A student takes data for a resistor and fits the straight line shown to the data. What is the resistance and the conductance of the resistor?
The slope represents the conductance.
14.8 mA - 0 mA1.48 mS
10.0 V - 0 VG
The reciprocal of the conductance is the resistance:
1 1 676 Ω
1.48 mSR
G
VR
I
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
23
Graph of Current versus Voltage
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 k
What is its conductance? 0.37 mS
Voltage (V)
Cur
rent
(m
A)
0 10 20 300
2.0
4.0
6.0
8.0
10
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
24
Graph of Current versus Resistance
If resistance is varied for a constant voltage, the current - resistance curve plots a hyperbola.
What is the curve for a 3 V source?
Resistance (k )
Cur
rent
(m
A)
0 1.0 2.0 3.00
2.0
4.0
6.0
8.0
10
V IR?
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
25
Application of Ohm’s law
26.8 mA
P o w er S u p p ly
+15 V- + - +5 V 2 A
D C A m m e te r
+-
G n d
V A
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
26
Linear
Ohm’s law
Troubleshooting
Characterized by a straight-line relationship.
A law stating that current is directly proportional to voltage and inversely proportional to current.
A systematic process of isolating, identifying, and correcting a fault in a circuit or system.
Selected Key Terms
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
27
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
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
28
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
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
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
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
30
Quiz
5. If the current in a 330 resistor is 15 mA, the applied voltage is approximately
a. 5.0 V
b. 22 V
c. 46 V
d. 60 V
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
31
Quiz
7. The circuit with the largest current is
a. (a)
b. (b)
c. (c)
d. (d)
R 10 k
+12 V R 15 k
+15 V R 22 k
+18 V R 27 k
+24 V
(a) (b) (c) (d)
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
32
Quiz
8. The circuit with the smallest current is
a. (a)
b. (b)
c. (c)
d. (d)
R 10 k
+12 V R 15 k
+15 V R 22 k
+18 V R 27 k
+24 V
(a) (b) (c) (d)
Chapter 2-3Chapter 2-3
Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd
T.Elsarnagawy, mde207, 311
33
Quiz
Answers:
1. d
2. a
3. b
4. b
5. a
6. c
7. a
8. c
9. d
10. c