Ch. 20

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

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

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

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

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)

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

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

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?

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

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.

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!

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

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

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 Main Menu