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Chapter 20 Electricity Section 1 Electric charge and static electricity Section 1 vocabulary • Electric force • Conduction • Electric field • Induction • Static electricity • Static discharge • Conservation of charge • Friction Electric charge • Charges that are the same repel each other. • Charges that are different attract each other. Electric force • Electric field • A region around a charged object where the object's electric force is exerted on other charged objects • Electric field around a single charge • Electric field around multiple charges Static electricity • Charges build up on an object, but they do not flow continuously Transferring charge • Charging by Friction • The transfer of electrons from one uncharged objected to another by rubbing • Charging by Conduction • The transfer of electrons from a charged object to another object by direct contact • Charging by Induction • Movement of electrons to one part of an object that is caused by the electric field of a second object • Detecting charge Static discharge • When a negatively charged object and a positively charged object are brought together, electrons transfer until both objects have the same charge. Section 2 Electric current Section 2 vocabulary • Electric circuit • Conductor • Insulator • Voltage • Voltage source • Resistance Flow of electric charges • What is electric current? • The continuous flow of electric charges through a material • Current in a circuit • To produce electric current, charges must flow continuously from one place to another. • An electric circuit is a complete, unbroken path through which electric charges can flow. Conductors and insulators • Conductors • A material through which charge can flow easily • Transfers electric charge well • Insulators • A material through which changes can not flow easily • Does not transfer electric charge well Voltage • Charges need energy to flow • Voltage • Potential difference • Causes a current in an electric current • Voltage sources • A device that creates a potential difference in an electric circuit Resistance • Current depends on resistance • Resistance is the measure of how difficult it is for charges to flow through a material. • The greater the resistance, the less current there is for a given voltage. • Factors that determine resistance • Path of least resistance Section 3 Batteries Section 3 vocabulary • Chemical energy • Battery • Chemical reaction • Wet cell • Electrochemical cell • Dry cell • Electrode • Electrolyte • Terminal The first battery • Luigi Galvani • Alessandro Volta • Volta built the first electric battery by layering zinc, paper soaked in salt water, and silver. Electrochemical cells • A simple cell • Electrochemical cell is a device that transforms chemical energy into electrical energy. • Electrodes are two different metals immersed in a substance • Electrolyte is a substance that conducts electric current • The part of an electrode above the surface of the electrolyte is a terminal • Chemical reactions occur between the electrolyte and the electrodes in an electrochemical cell. • These reactions cause one electrode to become negatively charged and the other electrode to become positively charged. Electrochemical cells • Batteries • A combination of two or more electrochemical cells in a series • Wet cells • An electrochemical cell in which the electrolyte is a liquid • Dry cells • An electrochemical cell in which the electrolyte is a paste Section 4 Electric circuits and power Section 4 vocabulary • Ohm's law • Series circuit • Ammeter • Parallel circuit • Voltmeter • Power Ohm's law • Ohm's results • Calculating with Ohm's law • The resistance is equal to the voltage divided by the current Features of a circuit • First, circuits have devices that are run by electrical energy. • Second, a circuit has a source of electrical energy. • Third, electric circuits are connected by conducting wires. Series circuits • One path • Resistors in a series circuit • Measuring current • An ammeter is a device used to measure current. Parallel circuits • Several paths • Resistors in a parallel circuit • Measuring voltage • A voltmeter is a device used to measure voltage, or electrical potential energy difference. • Household circuits Electric power • Power ratings • Calculating power • You can calculate power by multiplying voltage by current. Paying for electrical energy • The total amount of energy used by an appliance is equal to the power of the appliance multiplied by the amount of time the appliance is used. Section 5 Electrical safety Section 5 vocabulary • Short circuit • Grounded • Third prong • Fuse • Circuit breaker Personal safety • Short circuits • A connection that allows current to take the path of least resistance • Electric shocks • Grounding • One way to protect people from electric shock and other electrical danger is to provide an alternate path for electric current • A circuit is electrically grounded when charges are able to flow directly from the circuit into earth in the event of a short circuit. • The third prong, which is round, connects any metal pieces of the appliance to the ground wire of the building. Breaking a circuit • In order to prevent circuits from overheating, devices called fuses and circuit breakers are added to circuits. • A fuse is a device that contains a thin strip of metal that will melt if there is too much current through it. • A circuit breaker is a reusable safety switch that breaks the circuit when the current gets too high.