Chapter 19 Flow of Electricity Useful electricity requires moving electric charges You must do work to move a charged particle against an electric field

Electric Potential Difference the amount of work required to move a charge between two points unit of potential difference = volt (V) potential difference can be + or – depending upon the direction in which a charge is moving

Electron Flow

Electric Potential Difference trying to move a positive charge through a positive potential difference is like trying to roll a ball up a hill trying to move a positive charge through a negative potential difference is like rolling a ball down a hill Which is easier?

What Can Make Charges Move & Keep Moving? a device (such as a battery, thermocouple, or photocell) that uses a form of energy to do the work required to move the electric charge battery = chemical energy thermocouple = heat energy photocell = light (nuclear) energy

Conservation of Energy

Batteries converts chemical energy into electric energy each electrochemical cell contains two electrodes & an electrolyte the electrolyte (either a liquid or a paste) is a mixture of chemicals that produces a chemical reaction that releases electric charges

Wet-Cell Battery (Like a car battery)

Thermocouples converts heat energy into electric energy releases electric charges as a result of temperature differences the greater the temp difference, the faster the charges will flow used in car thermometers, ovens, & gas furnaces

Thermocouple

Photocells converts light energy into electric energy when light shines on a metal surface, electrons are emitted from the surface & can be routed through a wire

Circuit the complete path formed when a wire connects to the terminals of a source the flow of charge through a circuit is call an electric current

Current symbol for current = I units for current = ampere (A) amperes or amps are the amount of charge that flows past a point per second

Direct Current electron s always flow in the same directio n

Alternating Current electrons move back & forth, reversing their direction regularly

Georg Simon Ohm first person to establish the relationship between electric current & potential difference the current in a metal wire is proportional to the potential difference applied to the ends of the wire a greater potential difference means a greater current flow

Resistance opposition to the flow of electric charge symbol = R the amount of current that flows through a wire depends on the voltage & on how the wire resists the flow of charges electric charges are slowed by interactions with atoms in a wire copper wire is a good conductor so it has a very low resistance & allows charges to pass easily

4 Factors That Determine Resistance 1.type of material – more free e -, less R 2.length – longer means more R 3.width – thicker means less R 4.temperature – depends on material, some increase in R with higher temps while other have a decrease in R

Ohm’s Law states that the current in a wire is equal to the voltage divided by the resistance Current = voltage resistance I = V R Amperes = volts ohms

What are the amperes?

Electric Circuit a complete, closed path for an electric circuit

Parts of the Electric Circuit Source of energy (like a battery or generator) A load or resistance (like a light bulb or some other appliance that uses the electric energy) Wires for connection A switch that opens & closes the circuit

Remember that electricity cannot flow through an open circuit

when all parts are connected one after another & there is only one pathway for the electrons to travel any break results in the stopping of the current flow ever experienced this with holiday lights? Series Circuit

when different parts are on separate branches & there are several pathways for the electrons to travel any break in one branch does not completely stop the flow of electrons b/c they can still move through the other branches Parallel Circuit

Household Circuit Safety third prong on plugs – serves as a grounder b/c wire goes straight into the ground fuses – burn out when the passing current becomes to great (thin metal strip melt & breaks braking the flow) circuit breakers – a switch flips open (thus breaking the flow) when the current becomes too high

Electric Power a measure of the rate at which electricity does work or provides energy Power = voltage * current P (watts) = V (volts) * I (amperes) the higher the watts, the more energy (i.e. a brighter light bulb)

Electric Energy a measure of the total amount of energy used Energy = Power * Time kilowatt-hours = kilowatts * hours