current electricity. electrons p n nucleus e- flow of electrons (path) e-e- e-e- e-e- e-e- e-e- e-e-...
TRANSCRIPT
Current ElectricityCurrent Electricity
Electrons Electrons
Pn
nucleus
e-
Flow of Electrons (Path)Flow of Electrons (Path)
e-e- e-e-e-e-e- e-e-- +Electrons Flow Electrons Flow
Conventional CurrentConventional Current
e-
Conventional CurrentConventional Current
Flows Flows from from
+ + to to --
Current Current
Flow of ElectronsFlow of Electrons
Metals - Free ElectronsMetals - Free Electrons
e e e e e
CurrentCurrent
Flow of charge (q)!Flow of charge (q)!
q - Coulomb(C) q - Coulomb(C) 6.24 X 106.24 X 101818 electrons electrons
e ee e ee e e e e e eeee e
CurrentCurrent
e ee e ee e e e e e eeee e
Amount of charge passing Amount of charge passing a point in a second.a point in a second.
CurrentCurrent
Symbol - Symbol - II
Unit – Unit – Ampere (Amps)Ampere (Amps)
Amperes - Amperes - AA
Current =Current =ChargeChargeTimeTime
CurrentCurrent
CurrentCurrent = =ChargeChargeTimeTime
I =I =QQtt
CurrentCurrent
Ampere =Ampere =CoulombCoulombSecondSecond
1 A = 11 A = 1CCSS
ForceForce
e ee e ee e e e e e eeee e
VoltageVoltage
Potential DifferencePotential Difference
Electromotive Force (EMF)Electromotive Force (EMF)
Source of Electrons(Force) Source of Electrons(Force)
VoltageVoltage
Symbol - Symbol - VV
Unit – Unit – VoltVolt
Volt - Volt - VV
ResistanceResistance
Opposition to Current FlowOpposition to Current Flow
High ResistanceHigh ResistanceInsulatorInsulator
ResistanceResistance
Opposition to Current FlowOpposition to Current Flow
Low ResistanceLow ResistanceConductorConductor
ResistanceResistance
Opposition to Current FlowOpposition to Current Flow
High and Low ResistanceHigh and Low ResistanceSemiConductorSemiConductor
ResistanceResistance
Symbol - Symbol - RR
Unit – Unit – OhmOhm
Ohm - Ohm - ΩΩ
Putting it all TogetherPutting it all Together
LoadSource
Path
Schematic DiagramSchematic Diagram
I_
+V R
Source
Path
Load
Mathematical EquationMathematical Equation
I_
+V R
V = IR
Ohm’s LawOhm’s Law
Ohm’s LawThe mathematical
relationship betweenCurrent, Voltage and
Resistance.
Ohm’s Law WheelOhm’s Law Wheel
RIV
Find: V
V = IR
Ohm’s Law WheelOhm’s Law Wheel
RIV
Find: I
I = VR
Ohm’s Law WheelOhm’s Law Wheel
RIV
Find: V
R = V I
ExampleExample
I_
+V=10v R=500Ω
ExampleExample
Given: V=10v R=500Ω
RIV
Find: I = ?
I = VR
Equation: = 10V500Ω
I = 0.02A = 20mAI = 0.02A = 20mA
Homework:22-1Homework:22-1
Prob: 1,3,4,8,9, Prob: 1,3,4,8,9, 11,14,17,2011,14,17,20
Page 526, 527Page 526, 527Due: 3/20/07Due: 3/20/07
PowerPower
Power measures the rate Power measures the rate at which energy is at which energy is
transferred. In the case of transferred. In the case of electric current, charge is electric current, charge is
being transferredbeing transferred
PowerPower
Symbol - Symbol - PP
Unit – Unit – WattWatt
Watt - Watt - WW
PowerPower
Power = Current X VoltagePower = Current X Voltage
P = IVP = IV
Power WheelPower Wheel
VIP
Find: P
P = IV
Power WheelPower Wheel
VIP
Find: I
I = PV
Power WheelPower Wheel
VIP
Find: V
V = PI
Power EquationsPower Equations
VIP
P = V2
RRIV
P = IVP = I2R
Schematic SymbolsSchematic Symbols
ConductorSwitchFuseCapacitor
Resistor
Variable Resistor
Schematic SymbolsSchematic Symbols
Battery
dc generator
V Voltmeter
A Ammeter
Connection No Connection Ground
Schematic DiagramsSchematic Diagrams
Schematic DiagramsSchematic Diagrams
V
_
+R2
R1
V
A
Meter PlacementMeter Placement
Voltmeters are placed parallel to the component being
measured.
Ammeters are placed in series with the component being
measured.
Using Electric EnergyUsing Electric Energy
Energy used in an Electric Energy used in an Electric Circuit.Circuit.
P = E/tP = E/tE = PtE = Pt
Using Electric EnergyUsing Electric Energy
E = IE = I22RtRtE = IVtE = IVt
E = (VE = (V22/R)t/R)t
ExampleExample
_
+V=100v R=500Ω
How much energy is used How much energy is used in 1minute???in 1minute???
ExampleExample
Given: V=100v R=500Ω
t=1min=60s
Find: E = ?
E = V2t R
Equation:
E = (100V)2(60s) 500Ω
= 1200J1200J
Homework:22-2Homework:22-2
Practice Problems: Practice Problems: 11-1711-17
Page 517, 522Page 517, 522Due: 5/29/03Due: 5/29/03
Transmission ofTransmission ofElectric EnergyElectric Energy
Minimize Power Losses
P = I2RDecrease Current
Increase Voltage - 500,000V
The Kilowatt-HourThe Kilowatt-Hour
The Electric Company charges you for the amount of energy in
Kilowatt-Hours.
A Kilowatt-Hour is equal to 1000W delivered continuously for
1 hour(3600s).
The Kilowatt-HourThe Kilowatt-Hour
1kWh = (1000W)(1 hour) 1kWh = (1000J/s)(3600s)
1kWh = 3.6 X101kWh = 3.6 X1066 J J
E = PtE = Pt
Kilowatt-Hour ExampleKilowatt-Hour Example
A TV set draws 2.0A at 120V when operating. If the set is on 5
hours a day for 30 days, how much does it cost to run the set?
1 kilowatt-hour cost $0.12.
Kilowatt-Hour ExampleKilowatt-Hour Example
Given: V=120v I=2A
t=(5h/day)(30days)t=150h
Find: E = ? Cost
Kilowatt-Hour ExampleKilowatt-Hour Example
Equation: E = PtE = Ivt
E = (2A)(120V)(150h)E = 35000Wh = 35kWhCost = (35kWh)($0.12)Cost = $4.20Cost = $4.20
Homework:22-3Homework:22-3
Practice Problems: Practice Problems: 18-2018-20
Section ReviewSection ReviewPage: 525Page: 525
Due: 5/30/03Due: 5/30/03