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Transcript
Electricity and Magnetism The Atom Nucleus Protons Neutrons Electrons Rules Electric Charge and Polarity of Electric Charge More protons than electrons= positive charge More electrons than protons= negative charge Like= Repel, Opposite= Attract Electric Charge and Polarity cont… *In electricity, ONLY e- move, not protons!!* The strength of electric force= amount of excess + or – charge Electric Field: spot by charged particles where particles attract or repel Electroscope Demo Electric Fields Electric Field: area around charged particles where forces of attraction of repulsion exist Static Electricity Methods of Charging Friction- move electrons from 1 spot to another Conduction- transfers electrons through direct contact Induction- charged object forces change of charge in nearby object without contact Static Electricity cont… Lightning Particles move= buildup of charges - clouds= electrical charges on earth Causes electrons to jump from cloud to earth… lightning!! Thunder= air expanding due to heat of lightning Lightning is attracted to tall objects Static Electricity cont… Voltage The energy, or push that makes electrons move higher voltage = higher energy each electron carries Measured in unit called volt (V) Flow of Electricity Electric Current- flow of e- through a wire Current’s symbol is I Measured in amperes (A) higher current= higher e- Flow of Electricity cont… Resistance: opposition to flow of electricity Symbol is R Measured in ohms Poor conductors= high R ex. Iron Good conductors= low R ex. Copper R=Long and thin wires > short and thick Any device that gets plugged in is a resistor (load) Flow of Electricity cont… Ohms Law: I = V / R Direct Current (DC): electrons flow in the same direction ex. Batteries Alternating Current (AC): electrons constantly change the direction the flow ex. Electricity from power plants Electricity Circuits What is a Circuit?? Complete, closed path for electric current to flow Circuit only works when path is closed Parts of a Circuit A source of ea load (R), device that uses the electricity Wires to carry the electrons a switch opens or closes the circuit Electric Circuits cont… Series Circuit 1 path for current to flow All parts are connected one after another Same circuit passes through each resistor There would be a buildup of charge if not Ex. old Christmas lights Electric Circuits cont… Parallel Circuit Different parts of the circuit are on separate branches Several paths of electrons can be taken Ex. Newer Christmas light Electric Power Measure of rate at which electricity does work or provides energy P= V x I Units: Watts=Volts x Amperes 1 kilowatt = 1000 watts E= P x t Units: Kilowatt- hours= kilowatts x hours Meter reads kilowatt-hours Power Distribution Grid At the Power Plant Generators make 3 phase AD electricity via generators Electricity goes through a step-up transformer Voltage increased for travel over electric wires Voltage is usually stepped up to between 155000-765,000 volts!!! Power Distribution Grid cont… Transmissions of electricity High-voltage lines have huge steel wires Extras are for phone or support wires Electricity travels 300 miles from power plant Power Distribution Grid cont… Power Substation Can do several different things Have “buses”, split power in different directions Decrease voltage by using a step-down transformer Power Distribution Grid cont… Before going to the house Multi phase wires tapped to single phase Often see 3 wires going to house Transformer drum steps down 7200 v to 240 v Underground areas have a green transformer box above ground Power Distribution Grid cont… At the house Electric wires travel watt-hour meter 2 120 volt wires travel to circuit breaker Splits and is wired to all outlets of the house Magnetism Magnets have north and south poles Like poles repel, unlike poles attract Magnetic Field- where magnetic forces can act Earth has one, strongest at poles Magnetic lines of force define poles Electrons in atoms spin, causing magnetic field Magnetism Magnetic Materials Naturally occur Materials that are non-magnetized can become so: iron, nickel, and cobalt Earth as a Magnet Magnetosphere: region of magnetic field around Earth poles: geographical north=magnetic south Magnetism Compasses Needle of a compass is magnetic Compass needle points to north pole Electromagnetism Magnetism and electricity are inseparable Electromagnet: wind wire around an iron core Has north and south poles Magnet’s polarity depends on electric current’s polarity Magnetism and electricity induce each other Magnetism Electromagnets Electric wire wrapped around iron core Temporary Ex. magnets, turn on and off Junkyards, doorbells, telephones Magnetism Electric Motor Electric energy > mechanical energy (motion) Operates idea of reversal of polarity Has stationary permanent magnet, rotating electromagnet, and polarity reversing switch Magnetism Electric Generator Mechanical energy> electrical energy Conductor spins in a magnetic field Magnetic lines of force are cut by conductor Creates electricity, electro magnetic induction Power used everyday comes from generator Magnetism Galvanometer Detects electric current Wire coil connected to electric circuit w/ needle Current deflects needle towards direction of current Magnetism Galvanometer Electric Motor Electric Generator