Electrical Fields The space around any charged object is filled with an electrical field.The space around any charged object is filled with an electrical field. This field extends through space, much like a gravitational fieldThis field extends through space, much like a gravitational field Electric fields have both magnitude and direction, and so can be shown as vectors.Electric fields have both magnitude and direction, and so can be shown as vectors.

Electric Potential Electric charges have potential energyElectric charges have potential energy –By moving two positive charges closer together they gain electrical potential energy They want to release this energy much like a compressed spring.They want to release this energy much like a compressed spring. Electrical Potential = Electrical PE/Charge Units: joule/coulomb = volt (V) Since electric potential is measured in volts, it is called voltage

Energy Storage Electrical energy can be stored in a capacitor.Electrical energy can be stored in a capacitor. Capacitors store energy slowly and release it rapidlyCapacitors store energy slowly and release it rapidly Used inUsed in –Computers –Flashes –Televisions

Flow of Charge Charge flows when there is a potential difference, or difference in voltage, between ends of a conductor.Charge flows when there is a potential difference, or difference in voltage, between ends of a conductor. The flow will continue until both ends reach a common potential.The flow will continue until both ends reach a common potential. A flow of electric charge is called an electric current.A flow of electric charge is called an electric current. Bird on a wire…Bird on a wire…

Electric Current Current is measured in amperesCurrent is measured in amperes –The label is A, or amps. 1A = the flow of 1 coulomb per second1A = the flow of 1 coulomb per second When electrons flow through a wire, the number entering one end equals the number exiting the other endWhen electrons flow through a wire, the number entering one end equals the number exiting the other end

Voltage Source In order for charge to flow, a voltage source must be used to maintain a potential difference.In order for charge to flow, a voltage source must be used to maintain a potential difference. BatteriesBatteries –Wet cell –Dry cell GeneratorsGenerators

Resistance The flow of current depends on the electric resistance a conductor offersThe flow of current depends on the electric resistance a conductor offers For most conductors, increased temperature means increased resistance.For most conductors, increased temperature means increased resistance. Resistance is measured in ohmsResistance is measured in ohms Symbol: Symbol: 

Ohm’s Law Discovered by George OhmDiscovered by George Ohm Current is directly proportional to the voltage across the circuit and inversely proportional to the resistance in the circuit.Current is directly proportional to the voltage across the circuit and inversely proportional to the resistance in the circuit. Current = voltage/resistanceCurrent = voltage/resistance I=V/RI=V/R Units: volt/ohms = ampereUnits: volt/ohms = ampere

Ohm’s Law What is the resistance of a toaster that pulls 12 amps from a 120 volt circuit?What is the resistance of a toaster that pulls 12 amps from a 120 volt circuit? R=V/IR=V/I 120V/12amps = 10 ohms120V/12amps = 10 ohms How much current is drawn by a lamp that has a resistance of 100 ohms when it has a power source of 50V? I=V/R 50V/100ohms =.5 amps

Effects of current on the body Current in ampsCurrent in amps Effect Can be felt Painful Involuntary muscle contractions Loss of muscle control Probably fatal if it lasts for more than 1 sec.

DC vs. AC DC vs. AC Direct Current – Charge always flows in one direction.Direct Current – Charge always flows in one direction. –Electrons flow from negative to positive –Ex: Battery Alternating Current–Electrons move first in one direction, then in the other. –This is caused by alternating polarity. –Wall sockets provide AC

Using AC Most of the US uses AC voltage of V.Most of the US uses AC voltage of V. Europe uses VEurope uses V Some appliances, like electric stoves, use V.Some appliances, like electric stoves, use V. How can this be done in the US?How can this be done in the US? –Think about the number of holes in a wall socket.

Conversions Is it possible to operate a DC device on AC power?Is it possible to operate a DC device on AC power? Sure, you just need an AC/DC converter.Sure, you just need an AC/DC converter. These step down the voltage and contain a DiodeThese step down the voltage and contain a Diode A diode only allows electrons to flow in one direction. This gives choppy DC. Together with a capacitor, it provides good DC

Power Power is the rate at which electrical energy is converted to another form, such as heat, light, or mechanical energy.Power is the rate at which electrical energy is converted to another form, such as heat, light, or mechanical energy. Electric power = current x voltageElectric power = current x voltage P=IVP=IV 1 watt = 1A x 1V1 watt = 1A x 1V