Download Measuring Electrical Quantities

3-1
Electricity
Principles & Applications
Eighth Edition
Richard J. Fowler
Chapter 3
Basic Circuits, Laws,
and Measurements
(student version)
McGraw-Hill
© 2013 The McGraw-Hill Companies Inc. All rights reserved.
3-2
INTRODUCTION
• Circuit Symbols (p 46)
• Circuit Diagrams
• Parts of a Circuit (p 45)
• Measuring Electrical Quantities (p 53)
• Calculating Electrical Quantities (p 47)
(p 45)
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© 2013 The McGraw-Hill Companies Inc. All rights reserved.
3-3
Dear Student:
This presentation is arranged in segments. Each segment
is preceded by a Concept Preview slide and is followed by a
Concept Review slide. When you reach a Concept Review
slide, you can return to the beginning of that segment by
clicking on the Repeat Segment button. This will allow you
to view that segment again, if you want to.
McGraw-Hill
© 2013 The McGraw-Hill Companies Inc. All rights reserved.
3-4
Concept Preview
• Electrical components can be
represented by schematic symbols.
• A complete circuit needs a power source,
a load, conductors, and insulation.
• A schematic diagram doesn’t show the
physical layout of the components.
• Insulation, although required,
isn’t shown on a schematic diagram.
McGraw-Hill
© 2013 The McGraw-Hill Companies Inc. All rights reserved.
3-5
Symbol
Cell
Device
(p 46)
+ Terminal
Resistor
(p 43+)
Symbol
Device
Symbols and Components
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© 2013 The McGraw-Hill Companies Inc. All rights reserved.
3-6
This complete circuit uses the following:
(p 45)
•An energy or power source
•A control device
•A load
•Conductors
•Insulation (not shown)
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3-7
Constructing and Checking a Lamp Circuit
(p 58)
.
1 52
V-
mA
2
V
20

200
DC
2k
AC
20K
Cell
COM mA
V
Select and arrange the components.
Connect a wire from: 1) the cell to the switch,
2) the switch to the light, and 3) the light to the cell.
Connect the meter, and flip the switch.
McGraw-Hill
© 2013 The McGraw-Hill Companies Inc. All rights reserved.
3-8
Circuit Quiz
An electrical component has a ____ as
well as a name.
The long bar on the cell symbol is
the ____ terminal of the cell.
symbol
positive
A complete circuit has a ____ ____ that
forces current to flow.
power source
A complete circuit often has a ____ ____
that turns the circuit off and on.
control device
A complete circuit has a ____ that
controls the current flow.
load
A complete circuit has ____ that
route the current .
conductors
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3-9
Concept Review
• Electrical components can be
represented by schematic symbols.
• A complete circuit needs a power source,
a load, conductors, and insulation.
• A schematic diagram doesn’t show the
physical layout of the components.
• Insulation, although required,
isn’t shown on a schematic diagram.
Repeat Segment
McGraw-Hill
© 2013 The McGraw-Hill Companies Inc. All rights reserved.
3 - 10
Concept Preview
• Select the correct function on a
meter before making a measurement.
• Interrupt the circuit to measure current.
• Remove power from the circuit
before measuring resistance.
• Observe polarity when measuring
current or voltage.
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3 - 11
MEASURING VOLTAGE
(p 58)
Connect - lead to - terminal of source
Select the dcV
function
S1
B1
15 V
SPST
mV
V
mA
A

k
R1
dc
COM
-
+VA ac
1 k
Connect + lead to + terminal of source
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3 - 12
MEASURING CURRENT
(p 59)
Select the dc
mA function
S1
B1
15 V
SPST
mV
V
mA
A

k
R1
dc
COM
-
+VA ac
1 k
McGraw-Hill
© 2013 The McGraw-Hill Companies Inc. All rights reserved.
3 - 13
MEASURING CURRENT
(p 59)
Connect the - lead so
S1
B1
15 V
SPST
R1
Select the dc
mA function
that electrons enter it
Physically
interrupt the
circuit
mV
dc
1 k
McGraw-Hill
V
COM
mA
-
A

k
+VA ac
Connect the
+ lead to
the other
point
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3 - 14
MEASURING RESISTANCE
(p 57)
Select the k
function
S1
B1
15 V
SPST
mV
V
mA
A

k
R1
dc
COM
-
+VA ac
1 k
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3 - 15
MEASURING RESISTANCE
(p 57)
Remove power
(open switch)
S1
B1
15 V
Select the k
function
SPST
mV
V
mA
A

k
R1
dc
COM
-
+VA ac
1 k
Connect the
leads
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© 2013 The McGraw-Hill Companies Inc. All rights reserved.
3 - 16
Measurement Quiz
Select the correct ____ of the meter before
measuring an electrical quantity.
function
When measuring voltage, the meter’s positive lead
positive
is connected to the ____ terminal of the source.
When measuring current, the meter’s ____ lead
receives electrons from the circuit.
negative
When measuring ____ , the meter is connected to
the points created by interrupting the circuit.
current
Power is removed from the circuit before
measuring ____.
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resistance
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3 - 17
Concept Review
• Select the correct function on a
meter before making a measurement.
• Interrupt the circuit to measure current.
• Remove power from the circuit
before measuring resistance.
• Observe polarity when measuring
current or voltage.
Repeat Segment
McGraw-Hill
© 2013 The McGraw-Hill Companies Inc. All rights reserved.
3 - 18
Concept Preview
• Ohm’s law states that I = V/R.
• Rearrangement can yield V = IR.
• Rearrangement also yields R = V/I.
• Any of three formulae can be used
to calculate power.
McGraw-Hill
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3 - 19
CALCULATING CURRENT
(p 48)
S1
B1
36 V
SPST
R
1.8 k
V
36
V
= 0.02 A = 20 mA
I=
=
R
1800 
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3 - 20
CALCULATING
RESISTANCE
(p 49)
A
B1
24 V
0.03 A
R
V
24 V
R= I =
= 800  = 0.8 k 
0.03 A
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3 - 21
CALCULATING
VOLTAGE
(p 49)
A
B1
0.15 A
R
270 
V = IR = 0.15 A x 270  = 40.5 V
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3 - 22
CALCULATING
POWER
(p 49)
A
V
0.2 A
54 V
270 
P = IV = 0.2 A x 54 V = 10.8 W
P = I2R = 0.2 A x 0.2 A x 270  = 10.8 W
P = V2/R = (54 V x 54 V) / 270  = 10.8 W
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3 - 23
Calculation Quiz
Determine I when R = 10  and V = 25 V.
2.5 A
Determine R when I = 1.3 A and V = 26 V.
20 
Determine V when R = 15  and I = 1.2 A.
18 V
Determine P when I = 3.3 A and V = 16 V.
52.8 W
Determine P when I = 4 A and R = 20 .
320 W
Determine P when V = 8 V and R = 16 .
4W
McGraw-Hill
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3 - 24
Concept Review
• Ohm’s law states that I = V/R.
• Rearrangement can yield V = IR.
• Rearrangement also yields R = V/I.
• Any of three formulae can be used
to calculate power.
Repeat Segment
McGraw-Hill
© 2013 The McGraw-Hill Companies Inc. All rights reserved.
3 - 25
REVIEW
• Circuit Symbols
• Circuit Diagrams
• Parts of a Circuit
• Measuring Electrical Quantities
• Calculating Electrical Quantities
McGraw-Hill
© 2013 The McGraw-Hill Companies Inc. All rights reserved.