Electrical Quantities
Arch 433– Electrical Systems
Goals
To understand the basic terminology of
electricity
Be able to make basic electrical
calculations
Current Flow – Direction?
Electron Theory

Most negative to positive
(EurAsia)
 Most widely accepted as
being correct
Conventional Theory

Most positive to most
negative (US/Canada)
 Negative considered as
ground
 Positive as “HOT”

Schematics are drawn
from top down (positive
to negative
Electrical Quantities
Coulomb – (kü-läm-lōm)
Amp
Volt
Ohm
Watt
Horsepower
BTU
Electrical Quantities
Can humans create electricity?
• You would not be reading this if you
didn’t produce electricity
Electrical Systems
Electrical charges jump from one cell to
another in lieu of wires until they reach
their destination.
According to the Center for Space
Power and Advanced Electronics, the
human body is capable of producing
11,000 watt hours.
Electrical Systems
How many watts
•
•
•
•
•
•
81 watts sleeping.
128 standing at ease.
163 walking.
407 briskly walking
1,048 long-distance runner.
1,630 from a sprinter.
The Coulomb
cou·lomb
A quantity of measurement similar to a quart,
gallon, liter, etc.

It takes a certain amount of liquid to fill a gallon
One Coulomb = 6.25 x 1018 electrons

It takes a certain amount of electrons to equal a
Coulomb
One Coulomb = 6,250,000,000,000,000,000 electrons
6.25 Quintillion
The Coulomb
Coulomb's law or Coulomb's
inverse-square law is a law of
physics describing the electrostatic
interaction between electrically charged
particles. It was first published in 1785
by French physicist Charles Augustin de
Coulomb and was essential to the
development of the theory of
electromagnetism.
Charles Augustin de Coulomb
He liked to be
called
“Chuck” and to
his friends,
“Chucky C”
The Amp “I”
Defined -One Coulomb per sec

Note: involves a quantity and a time
One amp of current flows through a wire when
one coulomb flows past a point in one second
Noted as intensity of current or (“juice”,
“current”, electron “flow”)
The Amp “I”
• So Current is the flow…the flow of water
• Current (I) is equivalent to the flow rate, and
the resistance is like the pipe size.
• Increase the pressure, more water comes out
of the hose.
• Increase the diameter of the hose and more
water comes out of the hose
The Amp “I” (cont.)
Speed?
A single electron moves at a rate of 3
inches per hour at one ampere of
current flow
This is about as fast as my wife.
The Amp “I” (cont.)
The impulse of electricity can appear to be
faster than the speed of light

Knowing the speed of one electron, how can this
be?
When a ball (electron) is pushed at one end, another ball
(electron) at the other end is forced out.
There are billions of electrons in a wire – get the idea of
the impulse of electricity?
The Amp “I” (cont.)
It’s like a line dance!
The Amp “I” (cont.)
If a copper wire was wrapped around the
globe 10 times, it would take about 1.3
seconds to turn the light on at the other
end.
How do I know this?
Boat
Dessert
Bar
The Volt
“E”
Defined as electromotive force or EMF
Voltage cannot flow
 It is like pressure in a water system
 Voltage pushes current through a wire but DOES NOT
“flow” though a wire
The Ohm “” or “R”
The unit of resistance to current flow
An ohm is the amount of resistance that allows
1 amp of current to flow when the applied
voltage is 1 volt
Like a reducer in a water pipe or rough pipe vs
smooth pipe – restricts flow
The Ohm “” or “R” (cont.)
Heat caused by
the flow of current


Energy lost due to
electron contact
Resistance (similar
to friction heat)
The Watt “P”
A function of both voltage and amps


“push” and “amount of juice”
Known as “power”
Wattage is not a flow of current, it is a
resulting amount of power
Before true power can exist, there must be
some type of energy change or conversion


Heat (light bulb)
Mechanical (steam generator)
The Watt “P”
• Where did the term Watt come from?
• Actually you could say it came from
horses.
• Before we had electricity we had horses
working.
• Plowing fields and pulling carriages and
the like.
The Watt “P”
• And making a lot of horse poop. Or a
lot of horse crap …..or horse sh….
• However the word “lot” was confused
with “watt” as is in “a watt of crap” and
the term stuck.
• So when electricity was invented we
converted horsepower to the term
“watt”.
The Watt “P”
What (or watt) do you think? Could this
be possible true?
The Watt “P”
It’s false.
Class, meet Mr. James Watt
Hello class….I
like horses
Horsepower




James Watt needed to sell his steam
engines he was making.
So he put power in the term that people
would understand being horsepower
After experimentation, he found that the
average horse can work steady pulling a
plow at 550 foot-pound per second*
Doing the math, this would equate:
 1 hp = 746 W
*the amount of force required to raise one pound of weight one foot
Horsepower
So the term watt used in electricity
originated with James Watt trying to
find a way to measure something
people at the time understood which
was “horse power”. Horse power is the
amount of power an average plow
horse can exert.
Quiz Question
Where does the term “All balls out”
come from?
a) Ballroom dancing
b) A word used in the movie Animal House.
c) A part of the male anatomy
d) Firemen
e) None of the above
BTU – British Thermal Unit
Defined

The amount of heat required to raise the
temperature of one pound of water one
degree Fahrenheit
In metric terms, the joule is equivalent
to a watt
1 watt = 3.412 BTU per hour

1 kilowatt (kw) = 3412 BTU per hour
James Prescott Joule
I’m such a STUD
Conversion Chart - Power
Common Power Units
Electrical Quantities
E = Volts
I = Amps
R = Resistance
(Ohms  )
P = Watt
Ohm’s Law
Defined

It takes one volt
to push one amp
through one ohm
E=IxR
I = E/R
R = E/I
Georg Simón Ohm
Go Cougs!
Formula Chart
Ohm’s Law
Examples
R = 144
100 W
I = 0.83
V or E = voltage, I = current, R = Resistance
A light bulb rated at 100 watts. The bulb
operates at 120 volts
What is its current flow? 100w/120v =
0.83 ampere
What is the resistance of the filament?
120v/0.83a =
144 ohms,
or
1202/100W
= 144 ohms
Example (cont.)
R = 48
300 W
I = 2.5
A light bulb rated at 300 watts. The bulb
operates at 120 volts
What is its current flow?
300w/120v =
2.5 ampere
What is the resistance of the filament?
120/2.5 =
48 ohms, or
1202/300W
= 48 ohms
Example (cont.)
100 watt bulb has


0.83 amp current flow
144 ohms of resistance
300 watt bulb has

a bigger filament than 100 watt bulb thus
 2.5 amp current flow
 48 ohms of resistance
* A bigger filament means less resistance to electron flow.
This equates to more electrons passing through the
filament thus creating a more intense light
Practice Problems
An electric heating element has a resistance of 9.6  and is
connected to a voltage of 120 V. How much current will flow in
this circuit?
120v/9.6 = 12.5 A
Using the above question, how many watts of heat are being
produced by the heating element? (12.5 A)(120 V) = 1500 W
A 240 V circuit has a current flow of 20 A. How much power is
connected in the circuit? (240 V) (20 A) = 4800 W
An electric motor has an apparent resistance of 15 . If 8 A of
current are flowing through the motor, what is the connected
voltage?
(8 A)(15 ) = 120 V
Practice Problems (cont.)
You plan to install a 5 kW electric heating unit in your
home. You want to operate the unit in the most
efficient way. Would you connect the unit to a 120 V
or 240 V electrical system?
5000 W/ 120 V = 41.67 A
5000 W / 240 V = 20.8 A
In the above, which voltage system is the most
expensive to operate? Uses the most power? Uses
the most amperage? Uses the larger conductors?
Use same amount of power
120 V uses a larger current thus larger conductors
Problems (cont.)
A conductor has a resistance of 20 ohms per
1000 feet of length. The conductor serves a
lamp 200 feet from the power source. If
lamp has a resistance of 72 ohms and a
source voltage of 120, what is the voltage
drop across the light bulb?




First find ohms or resistance
Next circuit current
Next voltage drop through the conductors
Finally find actual voltage across the lamp
Problems (cont.)
4 + 72 + 4 = 80 ohms
120 V = (I)(80 ohms)
I = 1.5 A
E = 1.5 A (4 + 4) =
12 volts drop
E = (1.5)(72) = 108
volts
Questions
On a full sheet of paper and working with anyone
directly next to you place your names on that sheet.
Answer the following questions.
1) What is the maximum number of duplex outlets that
can be served by a single 20 ampere, 120 volt
circuit.
Going Bald……. Can cause
psychological issues
The research shows hair loss can
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• 62% of men affect their
self-esteem
• 43% of men to be concerned
with their attractiveness
• 37% of men to be worried about
getting older
• 22% of men to be anxious
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• 21% percent to become
depressed