Unit 6 – Lecture 1

Review3 types of subatomic particles

protons: + chargedneutrons: non-chargedelectrons: - charge

Equal p+ & e- = neutral atom or compound

Objects with no net chargeare called neutral

ChargeCharge – a point source of electrical force

two types – positive and negativeopposite charges attractlike charges repelmost objects are neutral

Conservation of ChargeLaw of Conservation of Charge

charges are neither created nor destroyed, they can only be transferred from one object to another

Review“Sea of Electrons” – elements in a metallic

bond do not hold their electrons tightly, but share them between all atoms

Static Chargestatic electricity –

the accumu-lation of excess electric [negative] charge on an objectstatic = not in

physical motion“static cling” –

objects that areoppositely charged “stick” together

Static Chargestatic electricity – the accumulation of excess

electric [negative] charge on an objectelectrons are being transferred

from the carpet to your shoeelectrical discharge – sudden

and momentary electric current between two objects

Static ChargeLightening is a form of static discharge

static charges are formed when the particles inside the storm cloud rub against each other [because of convection], separating charges.

Electric Fieldarea around a charged object which exerts

forces on other electric charges

ReviewConductor

a material through which electrons can move easily

best are metals [sea of electrons]

ReviewInsulator

a material through which electrons are not able to move easily

plastic, wood, rubber, glass…etc

Charging ObjectsCharge by Contact

transfer of charge by direct touch or rubbing

static cling

Charging ObjectsCharge by Induction

rearrangement of electrons in a neutral object because of a charge from a nearby object

ElectricityElectric Current [I]– the net movement of

electric charges in a single directionex: spark between you and doorknobmeasured in Amperes [A]

1 A = 6,250 million billion electrons per second passing a single point

ElectricityVolt (V) – unit of the PE of an electrical

chargeelectricity flows from that of higher voltage

to lower voltage

ResistanceResistance [R] – a material’s

opposition to the flow of currentmeasured in Ohms (Ω)resistance will turn

electrical E into thermal E and light

ResistanceResistance [R] – a material’s

opposition to the flow of currentconductor – less resistanceinsulator – more resistance

ResistanceIncrease resistance with…

increase temperatureincrease lengthdecrease thickness

ResistanceDecrease resistance with…

more, smaller batteriesshorter, thicker wiremore conductive metal

ElectricityOhm’s Law:

Current = Voltage / Resistance I = V / R

Voltage = Current * ResistanceV = I * R

Resistance = Voltage / CurrentR = V / I

V

I R

ElectricityPower (W) is measured in Watts

Power = Voltage * CurrentWatts = Volts * AmpsP = V * I

P

V I

PracticeThe current in a clothes dryer is 15 A when

plugged into a 240 V outlet. How much electrical power does the clothes dryer use?3,600 watts OR 3.6 kilowatts

Calculate the voltage difference in a circuit with a resistance of 50 Ω if the current of the circuit is 0.7 A.35 volts

ElectricityElectrical Energy is measured in kilowatt hours

[kWh]Electrical Energy = Electric Power * timeE = P * t

A microwave oven with a power rating of 1,200 W is being usedfor 0.25 h. How much electri-cal energy is being used bythe microwave?0.30 kWh

E

P t

HomeworkFor ALL problems, show ALL work:

1. Write Equation2. Plug In Numbers3. THEN Solve for Answer

ALL PROBLEMS MUST HAVE THESE THREE STEPS

Homework