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