Chapter 20 Electricity

Section 1 Electric charge and static electricity

Section 1 vocabulary Electric force Electric field Static electricity Conservation of charge Friction Conduction Induction Static discharge

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 Chemical reaction Electrochemical cell Electrode Electrolyte Terminal Battery Wet cell Dry cell

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.