Electricity and Magnetism

Electricity and MagnetismCh. 11 and 121

http://www.ecoprints.net/blog/environment/earth_night.jpgUsageEnergy Usage

Did you know that the typical U.S. family spends about $1,900 a year on home utility bills?large portion of that energy is wastedeach year, electricity generated by fossil fuels for a single home puts more carbon dioxide into the air than two average cars (US Dept. of Energy)History of Electricity1752: Benjamin Franklins kite experiment

1879: Thomas Edison and the light bulb

Late 1880s: small stations in cities

1930: larger towns and cities had, but only 10% rural farms

1935: Rural Electric Administration-President Franklin Roosevelts plan to bring electricity to all areas, especially rural farmersElectricityPresence of electric charges and their flow

Opposite charges attract and like repel

TypesStatic ElectricityAC and DCStatic ElectricityNo flow of electricityNegative (electrons) or positive (ions) charges accumulate on surface of object

If charges of two objects are opposite they will attract each other; like repelCoulombs LawThe electrical force that exists between 2 charged objects depends on their charges and the distance between them

F = k ((q1*q2) / d2)F=forcek=electric constantq=objects electrical charged=distance between objectsElectron FlowElectricity flows through wire when there is a voltage difference

A battery or a source of electricity is needed to complete the circuit so the current is able to flow through itElectrical ResistanceThe amount material resists flow of electricity (charged particles) through itMeasured in ohmsV = I * RV = voltage (volts)I = current (amps)R = resistance (ohms)

Toaster: 15-20 ohms resistanceHuman: dry-500,000; soaked in salt water-100examplesPractice ProblemsWhat is the current of flow through the lamp with a resistance of 60 ohm and a voltage of 12 V?

What is the resistance of an electric frying pan that draws a current of 12 A when connected to a 120 V circuit?Electric ShockNeed voltage difference to createSmall amounts are used for muscle therapyLarge amounts can result in death

Electric shock videoDirect Current (DC)Electricity flows in ONE directionElectrical circuit: source of DC electricity with a wire connecting it to an electrical device(s) and then back to the sourceTypical source is a batteryExample: flashlightRuns smaller devices

Alternating Current (AC)Electricity alternates direction back and forth (because the + and charge alternates)

Typical source is a generatorWire in homes is set up for ACVoltage can be changed (high voltage of power lines can be reduced for use in the home)Example: runs lights, computers, appliancesCircuitsSeries: everything is connected in a line

Parallel: devices are set up parallel to each other

Current is charged NOT the wireSeries CircuitUse: fuses in homes

If you increase devices connected the total resistance increasesCurrent is lowered in each deviceTotal energy or voltage is divided equally among the devices (so energy decreases for ea.)ParallelUses: car fans and the radio; lights

If you increase devices connected the total resistance decreasesTherefore current increases b/c voltage in each device is the same as what the source is producing

Calculating PowerAppliance-cost formula

Power (P-watts) = Current (I-amps) * Voltage (V-volts)

W = ?

Calculating Power

W = ?

What is the current traveling through a 60 W light bulb at 120 V?Overloading CircuitsMost outlets are 120 VIn parallel circuits:As more devices are plugged in the current through each device increasesToo much of an increase can lead to overloading and cause a fireGeneral circuits are connected to a fuse boxIf an overload occurs fuse blows and circuit breaks

Voltage in power lines is HIGH so the corresponding current is LOW and the line does not OVERHEATMagnetism vs. ElectricityHas north and south poles

North and south poles never exist on ownHas positive and negative charges

Positives and negatives (electrons and protons) can exist on ownCause objects to attract and repelSame strengthOpp. Attract; like repelMagnetismMagnetic fields: space around magnetCloser the lines stronger the fieldDirection of field is from North SouthField: produced by motion of ELECTRIC CHARGEMagnetic field is produced when electrons (electrical charge) move and ALSO spinMoving electrons have both electric & magnetic fieldsMagnetic Fields

Magnetic North Pole is in the South and the South Pole is in the NorthCompass: North attracts to Earths South mag. Pole and vice versaMagnetsBreak a bar magnet into two pieces each piece is magnetically as strongElectromagnetic InductionPass electric current through magnetic fieldResults in a stronger magnetCan produce large voltages (used in generators)How a junkyard magnet worksElectromagnetic Induction1831: Henry and FaradayDiscovered electric current can be produced by moving a magnet in or out of a wireAs increase number of loops of wire voltage increasesFaradays LawVoltage = # of coil loops * rate mag. field changesIncrease # of loops increase voltageElectromagnetic InductionTraffic LightsCar drives over buried wires, activates light

Security System at AirportChange in voltage by a metal object sounds an alarm

Credit Cards and Hotel room key cardMagnetic strip induced voltage pulses identify the cardUnit 3 TestBe able to:Calculate using ohms law (v=I*R)Calculate using the appliance cost/power equation (P=I*V)Understanding what Coulomb and Faradays laws meanKnow the basics of electricity and magnetism (how they work-charges)Basics about AC and DC Basics of parallel and series circuits**Study your notes if you take anyif any questions ask or look in ch. 11 or 12 in book