Electrical Quantities

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Electrical Quantities

• Arch 433 Electrical Systems

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Goals

• To understand the basic terminology of
  electricity
• Be able to make basic electrical calculations

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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

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Electrical Quantities

• Coulomb (kü-läm-lom)
• Amp
• Volt
• Ohm
• Watt
• Horsepower
• BTU

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Electrical Quantities

• Can humans create electricity?
• You would not be reading this if you didnt
  produce electricity

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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.

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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.

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The Coulomb coulomb

• 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
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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.

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Charles Augustin de Coulomb
He liked to be called Chuck and to his
friends, Chucky C
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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)

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The Amp I

• So Current is the flowthe 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

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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.

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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?
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The Amp I (cont.)

• Its like a line dance!

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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?

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Boat
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Dessert
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Bar
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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

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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

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The Ohm ? or R (cont.)

• Heat caused by the flow of current
• Energy lost due to electron contact
• Resistance (similar to friction heat)

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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)

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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.

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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.

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The Watt P

• What (or watt) do you think? Could this be
  possible true?

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The Watt P

• Its false.

Class, meet Mr. James Watt

Hello class.I like horses
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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
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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.

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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

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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

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James Prescott Joule
Im such a STUD
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Conversion Chart - Power
Common Power Units
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Electrical Quantities

• E Volts
• I Amps
• R Resistance (Ohms ? )
• P Watt

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Ohms Law

• Defined
• It takes one volt to push one amp through one ohm
• E I x R
• I E/R
• R E/I

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Georg Simón Ohm
Go Cougs!
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Formula Chart
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Ohms Law

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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?
• What is the resistance of the filament?

100w/120v 0.83 ampere
1202/100W 144 ohms
120v/0.83a 144 ohms, or
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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?
• What is the resistance of the filament?

300w/120v 2.5 ampere
1202/300W 48 ohms
120/2.5 48 ohms, or
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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
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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?
• Using the above question, how many watts of heat
  are being produced by the heating element?
•  
• A 240 V circuit has a current flow of 20 A. How
  much power is connected in the circuit?
•  
• An electric motor has an apparent resistance of
  15 ?. If 8 A of current are flowing through the
  motor, what is the connected voltage?

120v/9.6? 12.5 A
(12.5 A)(120 V) 1500 W
(240 V) (20 A) 4800 W
(8 A)(15 ?) 120 V
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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?
• In the above, which voltage system is the most
  expensive to operate? Uses the most power? Uses
  the most amperage? Uses the larger conductors?

5000 W/ 120 V 41.67 A
5000 W / 240 V 20.8 A
Use same amount of power 120 V uses a larger
current thus larger conductors
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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

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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
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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.
• What is the maximum number of duplex outlets that
  can be served by a single 20 ampere, 120 volt
  circuit.

48
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