Electricity

1
Electricity Principles Applications Sixth
Edition
Richard J. Fowler
Chapter 2 Electrical Quantities and Units
2
INTRODUCTION
Charge Coulomb Current Ampere
Voltage Volt Resistance Ohm
Power Watt
3
Electric Charge
Electric Charge
4
Electric charge is a property possessed by both
electrons and protons.
CHARGE (Q)
Quantity is
Base Unit is
COULOMB (C)
Examples of correct usage
Charge 15 Coulombs
Q 15 C
5
Current
6
Current is the movement of charge in a specified
direction.
Illustrations of current in a solid and a liquid
follow
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_ _ _ _ _ _ _ _ _ _ _ _ _

Ion
-
-

-

-
-
-

-

-
-
-
-
-
-



-
-
-
-
-


Ion
-
-
Ion
When an electron enters the charge area,
an electron must leave the - charge area.
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_ _ _ _ _ _ _ _ _ _ _ _ _

Ion
-
Ion
-

-

-
-

-

-
-
-
-
-



-
-
-
-


Ion
-
-
Ion
Ion
An electron moves from ion to ion.
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_ _ _ _ _ _ _ _ _ _ _ _ _

Ion
-
Ion
-

-

-

-
-

-
-
-
-
-



-
-
-
-


Ion
-
-
Ion
Ion
An electron moves from ion to ion.
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_ _ _ _ _ _ _ _ _ _ _ _ _

Ion
-
-

-

-

-

-
-
-
-
-
-



-
-
-
-


Ion
-
-
Ion
Ion
An electron moves from ion to ion.
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_ _ _ _ _ _ _ _ _ _ _ _ _

-
Ion
-

-

-

-

-
-
-
-
-
-



-
-
-
-


-
-
Ion
An electron moves from ion to ion.
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_ _ _ _ _ _ _ _ _ _ _ _ _

-
Ion
-
-


-

-

-
-
-
Ion
-
-
-



-
-
-
-


Ion
Ion
-
-
Ion
Ion
An electron moves from ion to ion.
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_ _ _ _ _ _ _ _ _ _ _ _ _

-
-
Ion
-


-

-

-
-
-
-
Ion
-
-



-
-
-
-


Ion
Ion
-
-
Ion
Ion
An electron moves from ion to ion.
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_ _ _ _ _ _ _ _ _ _ _ _ _
-
-
-


-

-
-

-
-
-
-
Ion
-
-



-
-
-
-


Ion
Ion
-
-
Ion
Ion
An electron moves from ion to ion.
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_ _ _ _ _ _ _ _ _ _ _ _ _
-
Ion
-
-


-

-

-
-
-
Ion
-
-



-
-
-
-
-


Ion
Ion
-
-
Ion
Ion
An electron moves from ion to ion.
16

_ _ _ _ _ _ _ _ _ _ _ _ _
-
Ion
-
-


-

-

-
-
-
Ion
-
-



-
-
-
-
-


Ion
Ion
-
-
Ion
An electron moves from ion to ion.
17

_ _ _ _ _ _ _ _ _ _ _ _ _
-
Ion
-

-

-

-

-
-
-
Ion
-
-



-
-
-
-
-


Ion
-
-
Ion
An electron moves from ion to ion.
18

_ _ _ _ _ _ _ _ _ _ _ _ _
Ion
Ion
-
Ion
-


-
-


-
-
-
-
-
-
-



-
-
-
-


-
-
Ion
Ion
Ion
An electron moves from ion to ion.
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Current in a Liquid
_

A salt electrolyte contains sodium ions and -
chlorine ions.
When the plates are connected to a source of -
and charges,
the ions move toward the plate with an opposite
charge.
20
Electric Current Terminology
Quantity is
CURRENT (I)
Base Unit is
AMPERE (A)
An ampere equals a coulomb per second.
Examples of correct usage
Current 12 Amperes
I 12 A
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Electric Current Relationships
Q
Charge
Current
I
t
Time
Examples
Q
14 C
1.4 A

I
t
10 s
Q
14 C
10 s

t
I
1.4 A
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Charge and Current Quiz
The base unit of charge is the ____ .
coulomb
The ____ is the base unit of current.
ampere
The symbol for current is ____.
I
The symbol for the coulomb is ____.
C
Current in a solid causes ____ to move from ion
to ion.
electrons
When Q 15 C and t 5 s, the current
equals ____.
3 A
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Voltage
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Definition of Voltage

• Voltage is the electric pressure or force that
  causes current.

• It is a potential energy difference between two
  points.

• It is also known as an electromotive force (emf).

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Voltage Terminology
Quantity is
VOLTAGE (V)
Base Unit is
VOLT (V)
A volt equals a joule per coulomb.
Examples of correct usage
Voltage 32 Volts
V 32 V
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Voltage Relationships
Energy
W
Voltage
V
Q
Charge
Examples
56 J
W
28 V

V
Q
2 C
84 J
W
4 C

Q
V
21 V
27
Voltage Quiz
Electromotive force is another name for ____.
voltage
The base unit of voltage is the ____.
volt
The symbol for voltage is ____.
V
The symbol for the volt is ____.
V
A volt is equal to a ____ per ____.
joule, coulomb
Q ____ when W 75 J and V 15 V.
5 C
W ____ when V 20 V and Q 2.5 C.
50 J
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Resistance
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Definition of Resistance
Resistance is the opposition a material offers to
current.
Resistance is determined by

• Type of material (resistivity)

• Temperature of material

• Cross-sectional area

• Length of material

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Some Factors That Determine Resistance
For a specific material and temperature, this
block has given amount of resistance.
Doubling the length of the block,
doubles the resistance.
Doubling the cross-sectional area,
halves the resistance.
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Resistance Terminology
Quantity is
RESISTANCE (R)
OHM (W)
Base Unit is
An ohm equals a volt per ampere.
Examples of correct usage
Resistance 47 ohms
R 47 W
32
Resistance Relationships
Resistivity x length
KL
Resistance
R
A
area
Example
1.4 x10-6 W cm x 2 x104 cm
KL

R
A
0.28 cm2
0.1 W
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Power
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Definition of Power
Power is the rate of using energy or doing work.

Using energy means that energy is being
converted to a different form.
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Power Terminology
Quantity is
POWER (P)
WATT (W)
Base Unit is
A watt equals a joule per second.
Examples of correct usage
Power 120 Watts
P 120 W
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Power Relationships
Energy
W
Power
P
t
Time
Examples
158 J
W
7.9 W

P
t
20 s
75 W x 25 s
W Pt
1875 J
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Resistance and Power Quiz
A materials opposition to current is called ____.
resistance
The base unit of resistance is the ____.
ohm
The symbol for the ohm is ____.
W
The rate of doing work is called ____.
power
The base unit of power is the ____.
watt
The symbol for the watt is ____.
W
P ____ when W 160 J and t 8 s.
20 W
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Multiple and Submultiple Units
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Conversion Between Base, Sub, and Multiple Units
.
.
A or 0.3 A
To convert 300 mA to A,
300 mA
move the decimal point three places to the left,
and change mA to A.
5200. J
5.200 kJ or 5.2 kJ
To convert 5200 J to kJ,
move the decimal point three places to the left,
and change J to kJ.
0.04 V
0040. mV or 40 mV
To convert 0.04 V to mV,
move the decimal point three places to the right.
and change V to mV.
40
REVIEW

• Charge Coulomb
• Current Ampere
• Voltage Volt
• Resistance Ohm
• Power Watt