1. Ch. 20

2. What is electricity? The energy from charged particles in atoms
Protons = + charge (pos.)
Electrons = - charge (neg.)
When it moves = electric current
When it doesn’t move = static electricity

3. Types of electrical current
(DC) Direct current electricity moves in one direction & usually is created in batteries
(AC) Alternating current electricity is most commonly used in homes & can have its voltage changed to suit the needs

4. Static Electricity Produced by a collection of stationary e-
Electrons are the easiest particles to move
Ex: When you walk on carpet & drag your feet, the ________ that takes places between your shoes & the carpet causes a build up of static electricity
Then you get a shock when you touch
something metal

5. Static Electricity cont.
After electrons are pulled away from a neutral item, it is left with a + charge
Static electricity is the collection of electrons & positive ions on the surface of a material--usually a non-conductor
_______ = + charge
_______= - charge

6. Charges Opposites charges (+ and -) attract each other
Charges that are alike (+ and +) repel
Conservation of charge
Charges are conserved just like energy is conserved (charges are transferred they don’t disappear)

7. accumulate on insulators
Conductors – material which electric charges can flow through easily (Ex: metal)
Insulator – material which electric charges cannot flow through easily or maybe not at all (Ex: plastic, rubber, wood)
Electrical cords are coated with plastic or rubber - you should not use a cord where the coating is damaged – you touch it & get shocked or it touches carpet or curtain & starts a fire
Static Elec. can only
accumulate on insulators

8. Electric Discharge – when electrons jump from a
Induction – an object’s electric field causes electrons to move to another object in close proximity (not touching)
Conduction – an object shifts some of its electrons to another object b/c they touched
Electric Discharge – when
electrons jump from a
charged to an uncharged object
Ex: Lightning

9. Circuits All electronic devices use circuits
Circuits are paths for electric current to flow through
Circuits are created by combining materials with different conductivity
Conductivity -Highest to lowest: silver, copper, aluminum, iron, silicon, water, glass, styrofoam
If H2O is not a top conductor- why not swim during a lightning storm?

10. Voltage, Resistance, & Current
Ohm’s Law – in ideal conductors, voltage is proportional to current & this relationship is expressed as a constant called resistance
V = I R
V is the voltage in volts
I is the current in amperes or amps
R is the resistance in ohms

11. Ohm’s Law Voltage - electrical potential energy, measured in volts
Think of a water hose = There is water pressure or potential energy on the other side of the faucet. Once you open the faucet, the pressure causes the water to rush through the hose.
Current - indicates amount of electrons passing through the wire, measured in amperes or amps, A.
Electrical current is similar to the rate of water flowing through a hose.
Resistance - can be thought of as the "friction" on the movement of electrons in a wire. Measured in ohms, omega, Ω.
Resistance is similar to the friction inside the hose. The resistance increases with a narrower hose or with a longer hose.

12. Electronic devices have resistors
If voltage increases, current also increases (assuming resistance stays the same)
Electronic devices have resistors
Ex: Toaster – the heating element is a piece of wire with greater Ω than copper. When the current gets to the wire heating element, the Ω increases & the current slows down, so the wire gets hot (looks orange-red) & toasts the bread!

13. Power
Watt ratings on light bulbs indicate how much power they need to work
Power – the rate at which electrical energy is supplied (measured in watts)
In simple circuits, Power is directly related to product of voltage & current
P = V I
Power = volts • amps

14. If a toaster has 120 volts & 2.3 amps, what is the Ω of the heating element?
R = V / I
R = 120 V / 2.3 A
R = 52 Ω
If the toaster is plugged into a standard wall outlet (120 volts) which supplies a current of 6A, how much power does the toaster use?
P = V • I
P = 120 V • 6A
P = 720 W

15. Electrical Circuits
Switches – the use it to turn something on or off – it does this by opening or closing a circuit
Off = open circuit (incomplete) current can’t flow through the circuit
On = closed circuit (complete) current can flow through it

16. 2 types: Series & Parallel
Series is basically a loop
If any part of the series fails,
everything is cut off

17. Complex series circuit – has more than 1 resistor in the circuit
Resistance increases each
time a resistor is added
& current decreases
I = V / R
R = inversely proportional to I
Rtotal = R1 + R2
Add up the resistors to find total resistance
Total voltage must = current needed for the sum of all resistors
Vtotal = I • Rtotal

18. Parallel circuit – resistors are wired so there are alternate paths to follow if 1 resistor fails
Christmas tree lights are like this – if 1 light goes out the rest stay lit
Your house is like this or else all the power would go off when you turned off 1 switch

19. Electromagnetism
Magnetism – general term for forces of attraction & repulsion
Magnetic field – where we notice these forces
Electromagnet is made when
electric current runs through
a wire loop that is surrounding
an iron core
Strength of the magnet is
directly related to # of coils
wrapped around the core

20. Mostly used in stereo speakers, electronics, motors & generators
Motor – converts electric energy into mechanical energy (ex: mixer)
Generator- converts mechanical energy
into electrical energy (ex: post storm)
Magnetic poles act
like electric charges
(poles called N & S)
Opposites attract
& like repel

21. Compass Earth has a magnetic field
Acts like a huge bar magnet runs through the center from N to S poles
Not exactly geographic N & S poles (these are in line with the
axis Earth spins on)
Compass points
toward magnetic
North

23.
Series and Parallel Circuit Lab
items needed
Aluminum Foil, small Christmas tree lights cut off a string of small Christmas tree lights with end of wire striped, 6 to 9 volt battery pack or power source, alligator clip wires, tape, scissors (Note if you do not have the alligator clips on the wire you can make a connection by wraping the bare wire in the foil.
Lights for this experiment
Battery pack - the pack can lack the aligator clips. If you donot have them, wrap the foil around the bare wire. you can find the parts to make this at Radio Shack - You moight have to let them know in advance to have enought battery packs to do this with a class. Do not use a 9 volt battery. they go dead to fast in this experiment to be of value to you
Notes Parallel and Series Circuit. One the student have cut out the foil pattern. they should connect the foil to the wire on the bulb by pushing the foil around the wire. Hook up the battery. Then disconnect a bulb . The other bulbs in the parallel circuit will stay on as there is another pathway for the electricity to flow. In the series circuit the lights will go out as there is only one way for the electricity to flow through the circuit.
Series Circuit Picture
Parallel Circuit Picture
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