AT 121
Chapter 3/4 - Part 2

Conductors 
•	Allow Electricity "Flow" 
•	Have three or less electrons, and they like to transfer!
•	Most Metals; Copper, Gold, Silver, Nickel
•	Water
•	Why?  Because they can transfer Electrons!
Insulators
•	Resist Electricity "Flow"
•	Have five or more electrons, and do NOT like to transfer!
•	Plastic, Glass, Air, Wood, Concrete
•	Cannot transfer electrons!
Electricity;
•	*IS* the movement of electrons!
•	Must be "pushed" by EMF;
•	Electro Motive Force

•	Protons at one end of circuit (+)
•	Electrons at other end of circuit (-)

•	The electrons are attracted to the protons

•	This causes atoms to transfer electrons to and from each other - but always in the *same* direction!
Two Types of Theories of how electrons move;

•	Conventional - Positive to Negative
•	Electron - Negative to Positive

•	IT DOES NOT MATTER FOR US!
3 Types of elements "control" electricity

•	Voltage = E (or V)
•	Current (Amperage) = I (or A)
•	Resistance (Ohms) = R (or Ω)
Voltage

•	Is electrical "force" or "pressure" that causes the electrons to move.
•	Big water pipe v/s Small water pipe
•	Voltage is the *difference* between Protons and Electrons in a power source
•	Overall electrical "potential energy“

•	House - 120 Volts
•	Car - 12 Volts (13-14 Volts)
•	Cooking Range  - 240 Volts
•	High Tension Line - 5,000 Volts
•	Lighting - 700,000 Volts

Current
•	Is electrical "rate" or "flow" of electrons.
•	Speed of river - Speed of flow
•	Current is the *rate* at which the electrons flow in a wire
•	Measured in Amperage (Amps or A or I)

•	House - 15 A per outlet 100 A total to the house
•	Car - 600 A!
•	Cooking Range – 40 A
•	High Tension Line - 5,000 Amps
•	Lighting - 200,000 Amps!
Resistance
•	Is "opposition" to current flow - AKA load
•	Rocks in river - Slowing down current!
•	Does the "work" in a circuit my making light, heat, or movement
•	Measured in Ohms (R) 

Several Factors of resistance are;
•	The atomic structure of the material 
•	Length of the conductor - Longer = Higher Resistance
•	Diameter of the conductor - Smaller = Higher Resistance

A Simple Circuit
Simple “Student” Circuits
•	Students = Electrons
•	This room, where you start
•	Voltage -The computer room, where you want to go - $100 dollars and free food 
•	There is quite a bit of pressure to get over there before the other students!  
•	And a lot of the other students are pushing you to move!
•	High current, you all stand up and rush.
•	Resistance…  The door.

Break.
Resistance
•	Resistance – You all slow down at the door.
•	The number of studelectrons running next door is slowed down
•	The *pressure* to get there, is still there, but now the *current flow* of students has slowed down!!
Resistance
•	Now… what if the hallway is reallllllly long, like 10 miles.. How many students are going to really, really finish?
•	Or, if there is a huge open pit… and students can’t make it across?
•	Or what if the hallway is 150 degrees.. And its long.. And I make you jump over pits….
•	How many are going to finish?  What happens to the *current* now?

How DC power is made
•	Chemical – Battery
•	Photoelectric – Solar Power
•	Thermoelectric – Engine Sensors!
•	Piezoelectric – BBQ Igniter – and more engine sensors!
•	Magnetic Field in Motion – Spinning Alternator

Magnets
•	Magnetic fields are the basis for most of the electronics in autos today.
•	Motion = magnetic fields 
•	N/S pole
•	Lines of Force
•	Natural and “Man” made
Electro Magnets.
•	As current (amps) flow inside a wire as part of a circuit (+ to -).
•	It Generates a magnetic field around the wire
•	Many turns of wire, in the same direction makes a bigger field.
•	More amps pushed into the wire makes a bigger field.

Remember what effects circuits!!
•	Amount of  Resistance
–	Length of wire
–	Temperature of Circuit
–	Type of work it does
•	Amount of Voltage
–	Pressure
•	Amount of Current
–	Rate of how fast the electrons move
Help online @ home;
•	http://science.howstuffworks.com/electromagnet.htm

•	http://science.howstuffworks.com/electricity.htm
Electrical Facts;
•	Voltage will “drop” as it moves into a load (the pressure to get to the 100$ bill is over.. Once you have it!).  There is less “potential energy”.
•	An increase in resistance causes a decrease in current.
•	All resistances change the electrical energy into heat energy to some extent.
•	All voltage must be "used up" in a complete circuit.
What is a circuit?

•	A path of electron flow consisting of;
•	A voltage source (Battery or Generator)
•	Conductors (Wires)
•	A load (Light Bulb)
•	And a return path (Wires back to the battery)

Simple Electrical - Symbols

Circuit "Terms"
•	Ground - "The end of the circuit" - The "lowest point" - No voltage is present at ground (because it got all used up – no more electrical potential!)
•	Open - No current flowing in circuit - due to a broken connection or a "open" switch
•	Short - "Shorted Path to Ground" - electrons bypass parts of the circuit and go right to ground!
A Simple Circuit

Watts
•	Named after James Watt
•	Measurement of heat, or electrical power
•	Is quite simply – P
•	P = Volts X Amps
•	P = E x I
Watts a real thing..
•	1200 Watts Microwave = 120 volts X 10 amps
•	Microwave
•	1200 or 800 Watt Microwave? 
•	Which one will cook your food faster by adding more heat?
•	Which one will run up more of your electric bill faster?

Homework.
•	1 – Worksheet 
•	2 – Answer review questions 1, 2, and 4
•	E-mail me answers or have them typed for the next class.
•	DON’T FORGET YOUR CALCULATOR!!