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https://www.youtube.com/watch?v=DCaN59knUCk
Electricity – movement electrons in a
material
Moves best through metals
Static electricity - collection of electrons &
positive ions on surface of a nonconductor
D.C. moves in one direction
usually is created in batteries
A.C. -most commonly used in homes &
can have its voltage changed as needed
Static Electricity
Usually produced by gathering a group of
stationary electrons
Electron have a _________ charge
Ex: When you walk on carpet & drag your
feet, the ________ that takes places b/t
your shoes & the carpet causes a build up
of static electricity
Then you get a shock
when you touch
something metal
Electrons = – charge
_______ = + charge
Opposites charges attract each other
Charges that are alike (two + or two –)
repel each other
Conservation of charge = ?
Charges are conserved just like energy is
conserved (charges are transferred)
Conductors – material which electric
charges can flow through easily (Ex:
metal)
Best conductors?
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?
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
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
Voltage, Resistance, & Current
Ohm’s Law – in ideal conductors, voltage is
proportional to current & this relationship is
expressed as a constant called resistance
V=IR
V is the voltage in volts
I is the current in amperes or amps
R is the resistance in ohms
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, as in 2.0A.
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. Three ohms is written as 3 Ω.
Resistance is similar to the friction inside the hose. But
also, the resistance increases with a narrower hose, just
like a thin copper wire has more electrical resistance
than a thick wire.
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 w/ 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!
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=VI
Power = volts • amps
If a toaster has 120 volts & 2.3 amps, what
is the Ω of the heating element?
R=V/I
= 120 V / 2.3 A
= 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 = VI
= 120 V • 6A
= 720 W
All electronic devices use circuits
Circuits are paths for electric current to
flow through
Circuits are created by combining material
w/ different conductivity (best conductors?)
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
2 types: Series & Parallel
Series is basically a loop
If any part of the series fails,
everything is cut off
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
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
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
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
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
http://www.kingsford.org/khsWeb/rfs/elemsci/circuit.html
http://www.kingsford.org/khsWeb/rfs/elemsci/circuit.html
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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