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.)

A single electron moves at a rate of 3 inches per hour at one ampere of current flowThis is about as fast as my wife.

Speed?

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 EMFVoltage 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 flowAn 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 watt1 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 = I x R I = E/R R = E/I

Georg Simón Ohm

Go Cougs!

Formula Chart

Ohm’s Law

Examples

V or E = voltage, I = current, R = Resistance

A light bulb rated at 100 watts. The bulb operates at 120 voltsWhat is its current flow?

What is the resistance of the filament?

100w/120v = 0.83 ampere

I = 0.83

1202/100W = 144 ohms

R = 144

100 W

120v/0.83a = 144 ohms, or

Example (cont.)

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

I = 2.5

1202/300W = 48 ohms

R = 48

300 W

120/2.5 = 48 ohms, or

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 ProblemsAn 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

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 A5000 W / 240 V = 20.8 A

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 AE = 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 cause:

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about their social life• 21% percent to become

depressed