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Electricity and Magnetism Chapters 20 and 21 Electric charge •Protons have a positive charge •Electrons have a negative charge •In most atoms, the protons equal the electrons No net charge •SI unit is Coulomb (C) Electric Forces •The force of Attraction or Repulsion Electric •How the charge affects Field the space around it + - •Atoms become charged by Static Electricity gaining or losing electrons •Excess electric charges on an object transfer to another object •Ex: shocking someone by rubbing electrons off the carpet. Lightning vs. Thunder Discharge of static electricity through grounding Easiest way for e- to move to the Earth Result of air expanding quickly Rules 1. Law of conservation of charge •Not created or destroyed, just transferred 2. Opposite charges attract. 3. Like charges repel Rules 4. Charges produce electric fields. Areas of attraction and repulsion 5. Electrons move more easily through conductors, like metals. Rules 6. Electrons do not move easily through insulators, like plastic. 7. Semiconductors: neither a good conductor or insulator, like silicon. Electric Current •Flow of charges through a conductor, usually a wire •Travels from a high voltage to a low voltage •Metric unit Amperes •Symbol I •2 types: Direct (DC) and Alternating (AC) •Opposes the flow of e- Resistance •Metric unit ohms (Ω) •Depends on length. Length Resistance •Depends on temperature. Temp. Resistance •Symbol R Voltage •Power of the charge •Batteries - source Dry cell (A, AA, C, or D) Wet cell (car battery) •Symbol V Ohm’s Law •V = I R Voltage = current x resistance •Units: Volts, amps, ohms •Hypothesized resistance reduces voltage Electric •A complete path through which electric Circuit charge can flow. Circuit •Symbols that represent Diagram the paths that the charges can flow. -switches demonstrate if the circuit is opened or closed Series Circuit •The current has only one path to flow through. •If any part of a series circuit is disconnected, no current flows through the circuit. Ex. Christmas Lights Lightbulb battery Parallel •Contains two or more Circuit paths for current to move through. lightbulb battery •Ex. Better Christmas lights Electric •The rate at which Power electrical energy is converted to another form of energy. •Electrical power is expressed in watts (W). •P = I x V Power = current x voltage Electric •How much energy that is Energy used to run appliances •E = P x t Energy = power x time Electric •Correct wiring, fuses, Safety circuit breakers, insulation, and grounded plugs help make electrical energy safe to use. •A fuse prevents an overloaded circuit •A breaker is a switch that opens when current is too high Magnetic •The force of a magnet Forces that attracts or repels •They have 2 strong ends: north pole and south pole Magnetic •A magnetic field (surrounds magnets) can Field either attract or repel other magnets that enter. Magnetic •The magnetic field that surrounds the earth is Field called a magnetosphere. •A compass will point North because it is in align with the Earth’s magnetic field Electro- •The force that usually magnetic results from charged particles Force •To control this force you need: *solenoid – a wire that carries current and produces a magnetic field •Changing the current strengthens the magnetic field Devices •Galvanometer – measures small amounts of current *Ex. Fuel Gauge •Electric Motor – turns an axle *Runs a motor Loudspeakers – contain a solenoid placed around a pole of a permanent magnet •A magnetic field is used to Electroproduce an electric magnetic Induction current. •Voltage is induced in a conductor by changing fields in a complete circuit. Generators Transformers •Rotates a coil of wire in a magnetic field to produce current. •2 types: AC and DC •Change or transform amounts of voltage by alternating current •2 types: step-up and step-down