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Electric ChargesAlittlechemistry All matter Atoms areis made up of atomsmade of protons,neutrons, and electrons Protons: (+) Neutrons ( no charge ) Electrons: (-) Atoms can have a positivecharge,anegative charge, or no charge at all.Charges Electrical charge caused by animbalance of protons and electrons Positive (more protons than electrons) Negative (more electrons than protons) Neutral (same number of protons and (Electric Fields of each shown above) Opposites attractelectrons)LikesrepelMoreChemistry Acharge can never be created or destroyed.It is transferred from one object to another.This happensto anotherwhenelectronsmovefromoneobjectOppositeChargeLike ChargeTransferring ChargeElectric energy is never created or destroyed,only transferredObjects (generally those that arecan become charged by one of 31. Induction2. Conduction3. Frictionconductors)ways:Transferring ChargeInduction Transferring a charge by bringing acharged object NEAR a neutral object withouttouching it.The total charge on the door knob will still be neutral, but the opposite sides will have opposite chargesTransferring ChargesConduction - Electrons are transferred from oneobject to another by contact, or touching.When a negatively charged rod touches a neutral door knob, electrons transfer from the rod to the doorknob to give the doorknob a negative chargeTransferring ChargeFriction - two objects rub up against each other,leaving electrons built up on one side. Bothobjects become charged.i.e. rubbing a balloon on your head, walking acrosscarpet, wool rubbing on metalStatic Discharge John Travoltage!! http://phet.colorado.edu/en/simulation/travoltageControlling the Path of Electric ChargeElectrical Conductor: a material in whichcharges move freelyi.e. metal (wires) and waterElectrical Insulator: a material in whichcharges cannot move freelyi.e. plastic, wood, glass, foam, cloth, ceramicControlling the Path of ElectricChargeElectrical Conductor:the metal inside the cord presentsapath of little resistancecharge to flowfor theElectrical Insulator:the rubber/plastic has a highresistance, to keep the charge from leaving the metal path of wire(and to ensure you dont shock yourselfwhen you touch the cord!)CURRENTS AND OHMS LAWWhat? Electricity flow of electric current Electric current themovementofanelectrical charge. In most cases, wethink of an electric current running through a circuit. In comes Ohms Law.Ohms LawV = I x RV = Voltage (units are volts, v)I = Current (units are ampres, A)R = Resistance (units are ohms, )Voltage Voltage is the difference inbetween two places where A negative charge (electron)from other negative chargeselectrical potentialelectrons are flowing.wants to move away(other electrons.) These repulsive forces increase as electrons are closer toeach other. Electrons flow from high potential energy to low potential. This potential difference is usually just called voltage Voltage provides the energy that pushes and pulls electrons through the circuit. Voltage is measured in Volts (V)Batteries Batteries can have differentvoltage, and therefore pushdifferent strength currents Range from 1.5 volts to 12 volts Batteries have a positive terminaland a negative terminal. Electrons are pushed from the negative terminal and are pulled towards the positive terminal BUT current is in the opposite directionVoltage BasicallyVoltage is difference motionVoltage ispotentialelectricalthat sets a charge inthe PUSH and is measuredin Volts (V)Current: General Idea An object moving in a specific direction Current can be water, air, cars, or charge Current is caused because of a difference pressure on either side of an objectin Once the difference in pressure is gone, current stops Pumps & Batteries are used to maintain a difference inpressure.ElectricCurrent Just as water current is flow of water molecules,electric current is the flow of electric charge. Measured in Amperes (A) In metal circuits, movingflow of charge. Electrons travelnegative to positive Current travels inelectronsmakeupthethe OPPOSITEas electrons do.directionTypes of CurrentTHERE ARE TWO TYPES OF CURRENT:In a direct current (DC) the current always movesterminal to the other in the same direction.- example: batteryfromoneIn an alternating current (AC) the current willalways alternate directions at regular intervals.- example: appliances at homeRemember, direction of the current isopposite the direction of electron flow.VoltageandCurrent Voltage PUSHES charges through circuits. Current is how fast electrons FLOW thru the Example you could say thatcircuit Amps measure how much water comes out ofa hose. Volts measure how hard the waterhose.comesoutofa Basically: As Voltage Increases,Current Increases!Practice!So how does this relate to awesome computer simulations?http://phet.colorado.edu/en/simulation/ohms-lawResistance (R) Objects use different amount of powerbecause they have different amounts ofcurrent running through them. The difference in current is due to theresistance.Resistance (R) Resistance: the tendency for a material to oppose theflow of electrons, changing electrical energy intothermal energy and light. Resistancemovementis caused by internal friction, which slows theof charges through a conducting material. Resistanceis measured in Ohms ().Resistance and Wires Conductors have low resistance The better the conductor, the better that electrons willmove through the material in thefield ie: metal wirespresenceofanelectric Insulators have high resistance The better the insulator, the more that the substance will resist the movement of electrons. ie:plastic or rubberResistance (R) The resistance of a light bulb filament determines howbright the bulb will be The filament of a 40watt bulb has a much higher resistance than a 100watt bulb This is because more resistance = less current = dimmer bulb So being able to control resistance would be agood thinga wire: 2 ways make makethat we can increase resistance inthe wire longer (ie: the loops)wire thinner Thicker wire = less resistance Thin wire = more resistanceOhms LawV = I x RV = Voltage (units are volts, v)I = Current (units are ampres, A)R = Resistance (units are ohms, )Practice!The headlights of a typical car are powered by a 12Vbattery.What is the resistance of the headlightsifthey draw 3.0 A of currentwhenturnedon?Use your Ohms Law Triangle---Insert your valuesUse unitsSolve!SERIES AND PARALLELCIRCUITSCircuits Provides a path for electricity to travelSimilar to water pipes in yourBecause of the voltage of an will travel through the circuithouseoutlet,electrons Electrons NEED to travelaround the ENTIRE pathfor anything to workOpen vs.Closed Circuits When there isclosed circuit. When there isa complete path, the circuit is consideredaNOT a completepath,thecircuitisconsideredanopencircuit. A switch allows you to openand close a circuitConductive Ink!!! The ink on this page conducts electricityink).(yes, it is special Whatover? happens to the whenthepageisfoldedtoto tothethe thecircuit?lightbulb?current?

Safety Precautions If too many devices (tv, radio, hairconnected to an outlet, the overall circuit is lowered This increases the current travelingdryer, etc) areresistance of thethrough thecircuit, possibly more than a safe level This is called an overloaded circuit.ofcurrent. Too much current traveling thougha wire can cause fires.when tooSafety Precautions Both of these objects open the circuit by disrupting the completecircle, preventing damage to the rest of the circuit. FUSE a ribbon of metal wirethatmeltsmuch current flows through If current becomes too high,the fuse melts, and the circuit is open Can only be used oncethen must be replaceditSafety Precautions Circuit Breaker opens a circuitwith a high current Uses an electromagnet that responds to current overload by opening the circuit Basically it is magnetic switch that trips The circuit breaker acts as a switch. Can be used multiple times.reset once tripped.Must beCircuitDiagrams Uses symbols to represent parts of a circuit Shorthand way todescribe a realcircuitCircuitSymbols:HowtoDrawOnOffSwitchElectricalSupply(Battery)ResistorLightBulbRemember, the circuitdrawing needs to be a COMPLETEpath.CircuitSymbols:HowtoDrawYou trytodrawsomecircuits:A circuitswitch.withoneresistor, one battery,andone1.A circuitwithtworesistors, three batteries, and2.one switch.Circuits: 2 Diff TypesCaneitherbeseriesorparallel.Series:1 pathParallel: 2+ PathsResistance ()Overview:SeriesvParallelCircuitsMUST CALCULATE(Voltage drops to 0v afterSeriesParallelPathways for electronsand currentOnly 1 path.Multiple Pathways for currentCurrent (I)Always the same throughoutDifferent at each branch Voltage (V)VOLTAGE DROP after everyresistor/bulb: MUST CALCULATE each separatelyEach Branch startswith same voltageeach branch)Add up all to get totalEach branch different - MUST CALCULATE each branchLets Practice: Identify WSTry some drawings! 1) Series: with 2 resistors (one is 4 ohm,12V battery, and a 10 ohm light bulb.one is 7ohm), a 2) Parallel: with a 1.5 volt battery and 3 light bulbs(each on its own branch). Light bulbs have a resistanceof2, 4, and 6 ohms. 3)Series: 6v battery, one switch, one 20ohm resistor. 4)Parallel: 12volt battery, 3 light bulbs.2 light bulbs (23rdand 3 ohms) are on one branch, while the(8ohms) is on another branch)light bulbCircuits: 2 Diff TypesCaneitherbeseriesorparallel.Series:1 pathParallel: 2+ PathsSeries circuits There is only 1 path forcurrent/electrons to travel If the circuit opens in any way, the whole circuits stops working because current STOPS.Series Circuits Current only takes one path for electronsIfyou remove a light bulb or one burnsoutthe ENTIRE circuit stops working! Current stays the sameas it flows through everypart ofthe circuit Resistance (and thereforevoltage), will change at different points on a series circuitCurrent in Se

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