Electricity

Means a flow of charge (like a water current indicates flow of water) Electric current is based on quantity of charge per second Current (I) = charge (q) / time (t) I = q/t Unit is coulomb per second, called ampere, or amp for short Electric current

Simple Circuit

Substance that allows charges to flow easily Metals- good conductors Wood/plastic/rubber/diamond/glass- poor conductors Good conductors have low resistance and vice versa Conductors

Electrical resistance is property of opposing or reducing current Depends on four variables: Material Length (longer has greater resistance) Diameter (thinner has greater resistance) Temperature (increased temp greater resistance) Resistance

An electrical circuit contains a device, such as a battery or generator, that acts as a source of energy as it forces charge out of one terminal, through the wires of the circuit, and back into the other terminal. Work is done by electric field generator (ie. battery) Work done by device (ie. Lamp) is equal to work done on battery Voltage (V) is ratio of work to charge moved V=W/q 1 volt (V) = 1 joule (J) / 1 coulomb (C) Voltage

Electric Circuits

Volt = joule/coulomb 1 V = 1 J/1 C Household circuits typically have 120 or 240 volts V of 120 means that each coulomb of charge that moves through the circuit can do 120 J of work in some electrical device Is there anything that might limit work? resistance Units of electric circuit

If conductor offers small resistance, less voltage needed to push an amp of current through circuit More resistance requires more voltage Resistance is ratio between voltage and resulting current R=V/I………………….1 ohm = 1 volt/1 amp Resistance units are ohms (  ) Rearrange equation to get V=IR, this is known as Ohm’s law Resistance

Ohm’s Law Voltage (V) Resistance (R) Current (I)

All circuits have three parts in common Voltage source, device where work is done, conducting wires Resistance impacts work done (like friction), so we use low resistance conducting wires Power output is determined by voltage, current, time Power =Voltage * Current P = joule/coulomb times coulomb/sec yielding joule/sec A joule/sec is called a watt Electrical power and work

Voltage usually 120 or 240 Lightbulb might have power of 100 W Cost varies, usually in cents per kilowatt-hour Cost = (watts)(time)(rate) 1,000 watt/kW Electrical power and cost