LCHS Physics Mark Ewoldsen, Ph.D. Definitions Voltage: Electric Potential or Potential Difference...
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Transcript of LCHS Physics Mark Ewoldsen, Ph.D. Definitions Voltage: Electric Potential or Potential Difference...
LCHS PhysicsLCHS PhysicsMark Ewoldsen, Ph.D.Mark Ewoldsen, Ph.D.
DefinitionsDefinitions
• VoltageVoltage: Electric Potential or Potential : Electric Potential or Potential Difference (Energy added or used)Difference (Energy added or used)– V (volts) = Joules/Coulomb V (volts) = Joules/Coulomb
– One volt = one coulomb of charge gains One volt = one coulomb of charge gains or loses one joule of energyor loses one joule of energy
What is the difference between E and V?What is the difference between E and V?
• E is the voltage supplied by a batteryE is the voltage supplied by a battery
• V is the voltage measured across a resistorV is the voltage measured across a resistor
BatteriesBatteries• Positive and Negative terminals Positive and Negative terminals
– electrons leave negative terminalelectrons leave negative terminal
• Batteries use a chemical reaction to create Batteries use a chemical reaction to create voltagevoltage
• Construction: Two different metals and AcidConstruction: Two different metals and Acid– e.g. Copper, Zinc, and Citrus Acide.g. Copper, Zinc, and Citrus Acid
– e.g. Lead, Lead Oxide, Sulfuric Acide.g. Lead, Lead Oxide, Sulfuric Acid
– e.g. Nickel, Cadmium, Acid Pastee.g. Nickel, Cadmium, Acid Paste
DefinitionsDefinitions
• CurrentCurrent: Flow of electric charge: Flow of electric charge– I (amps) = Q/t = Coulombs/secondI (amps) = Q/t = Coulombs/second
– Higher current increases heat due to more Higher current increases heat due to more collisions of ‘free’ electrons with atomscollisions of ‘free’ electrons with atoms
Effect of Currents on the BodyEffect of Currents on the Body
• 0.001 A can be felt0.001 A can be felt
• 0.005 A is painful0.005 A is painful
• 0.010 A0.010 A causes involuntary muscle causes involuntary muscle contractionscontractions
• 0.015 A causes loss of muscle control0.015 A causes loss of muscle control
• 0.070 A can be fatal if the current last for more 0.070 A can be fatal if the current last for more than 1 second than 1 second
Speed of Electrons in CircuitSpeed of Electrons in Circuit
• Light goes on ‘instantly’ when switch turned onLight goes on ‘instantly’ when switch turned on– Electrons do not move at speed of lightElectrons do not move at speed of light
• c = 3 x 10c = 3 x 108 8
• Electrons – 6 x 10Electrons – 6 x 1055 m/s in random directions m/s in random directions
– Signal (energy) moves at speed of light due to electric Signal (energy) moves at speed of light due to electric energy fieldenergy field
• Wire acts as pipe to guide electric fieldWire acts as pipe to guide electric field
• Electrons in circuit do not come from battery but Electrons in circuit do not come from battery but are from the wireare from the wire
DefinitionsDefinitions• ResistanceResistance: : measure of a material’s ability measure of a material’s ability
to resist the flow of of electronsto resist the flow of of electrons– ΩΩ (ohms) = J-s/C (ohms) = J-s/C22
– Conductor – low resistanceConductor – low resistance• materials with free electronsmaterials with free electrons• e.g. copper, aluminum, gold, most metalse.g. copper, aluminum, gold, most metals
– Insulator – high resistanceInsulator – high resistance• materials with no free electronsmaterials with no free electrons• e.g. glass, plastics, ceramics, woode.g. glass, plastics, ceramics, wood
DefinitionsDefinitions• ResistanceResistance
– Increases with length Increases with length – L– L – Decreases with cross area Decreases with cross area – A – A – ResistivityResistivity – – ρρ
• material material dependentdependent • temperature dependenttemperature dependent
R = R = ρLρL AA
DefinitionsDefinitions
• PowerPower is the rate energy is converted is the rate energy is converted into another forminto another form– Resistors transform electrical energy into Resistors transform electrical energy into
light, mechanical or heat energylight, mechanical or heat energy
• Equation for Power:Equation for Power:P = I V P = I V
(Watts) – Joules/second(Watts) – Joules/second
DefinitionsDefinitions
AAmmeterAmmeter: measures amp(ere)s: measures amp(ere)s
BatteryBattery: Source of energy: Source of energy
ResistorResistor: Removes energy: Removes energy
VVoltmeterVoltmeter: measures volt(age): measures volt(age)
WiresWires::
Reading a Voltmeter Reading a Voltmeter
Reading a Ammeter Reading a Ammeter
Making CircuitsMaking Circuits
Making CircuitsMaking Circuits
A
Making CircuitsMaking Circuits
A
V
Making CircuitsMaking Circuits
A
V
V
V
A
How many batteries?How many batteries?
V
A
How many ammeters?How many ammeters?
V
A
How many voltmeters?How many voltmeters?
V
A
How many light bulbs?How many light bulbs?
Ohm’s Law:Ohm’s Law:V = I RV = I R
V = voltage, I = current, R = resistanceV = voltage, I = current, R = resistance
For a given voltage, as the resistance goes up, For a given voltage, as the resistance goes up, the current will go downthe current will go down
OR
If the resistance is less, the current is moreIf the resistance is less, the current is more
Ohm’s LawOhm’s Law
V
A
Ohm’s LawOhm’s Law
V
A
Constant VoltageConstant Voltage• For a given pressure on a car’s acceleratorFor a given pressure on a car’s accelerator
– Voltage or energy inputVoltage or energy input
• By increasing the steepness of a hillBy increasing the steepness of a hill– Changing resistanceChanging resistance
• The car’s speed will go downThe car’s speed will go down– Decrease the current or ampsDecrease the current or amps
Turned on
When light is first turned onWhen light is first turned on• Filament is coldFilament is cold
– The resistance is low andThe resistance is low and– since V = IR, current is highsince V = IR, current is high
• High current means filament is more likely High current means filament is more likely to burn outto burn out
Ohm’s Law:Ohm’s Law:V/I = RV/I = R
V = voltage, I = current, R = resistanceV = voltage, I = current, R = resistance
For a given resistance, as the voltage For a given resistance, as the voltage goes up, the current goes upgoes up, the current goes up
Ohm’s Law – Set ResistanceOhm’s Law – Set Resistance
A
V
A
V
A
V
A
V
http://www.physics.udel.edu/wwwusers/watson/scen103/98w/note0105.html
In a simple one resistor circuit, what is In a simple one resistor circuit, what is the Resistance if the Voltage is 12-V and the Resistance if the Voltage is 12-V and
Current is 3-A?Current is 3-A?
In a simple one resistor circuit, what is In a simple one resistor circuit, what is the Resistance if the Voltage is 120-V the Resistance if the Voltage is 120-V
and Current is 5-A?and Current is 5-A?
In a simple one resistor circuit, what is In a simple one resistor circuit, what is the Voltage if the Resistance is 12-the Voltage if the Resistance is 12- and and
Current is 3-A?Current is 3-A?
In a simple one resistor circuit, what is In a simple one resistor circuit, what is the Voltage if the Resistance is 3-the Voltage if the Resistance is 3- and and
Current is 17-A?Current is 17-A?
In a simple one resistor circuit, what is In a simple one resistor circuit, what is the Current if the Resistance is 3-the Current if the Resistance is 3- and and
Voltage is 17-V?Voltage is 17-V?
In a simple one resistor circuit, what is In a simple one resistor circuit, what is the Current if the Resistance is 3-the Current if the Resistance is 3- and and
Voltage is 120-V?Voltage is 120-V?
Series CircuitSeries Circuit
Finding V, I & R for a Finding V, I & R for a Series CircuitSeries Circuit
1.1. Determine total E (V from battery)Determine total E (V from battery)2.2. Find the total Resistance Find the total Resistance
RRT T = R= R11 + R + R2 2 + R+ R33 … …
3.3. Determine IDetermine ITT by by
I = VI = VTT/R/RTT
3.3. Since I is constant in a series circuit, find Since I is constant in a series circuit, find V (energy used) by each resistor using V (energy used) by each resistor using
V = IV = ITTRR
Finding V, I & R for a Finding V, I & R for a Series CircuitSeries Circuit
1.1. Determine E (V from battery)Determine E (V from battery)
12 V12 V
1 Ω2 Ω
3 Ω
Finding V, I & R for a Finding V, I & R for a Series CircuitSeries Circuit
1.1. Determine E (V from battery)Determine E (V from battery) - 12V- 12V2.2. Find the total ResistanceFind the total Resistance
RRT T = R= R11 + R + R2 2 + R+ R33 … …
12 V
1 1 ΩΩ2 2 ΩΩ
3 3 ΩΩ
6 6 ΩΩ = = 3 3 ΩΩ + + 2 2 ΩΩ + + 1 1 ΩΩ
Finding V, I & R for a Finding V, I & R for a Series CircuitSeries Circuit
1.1. Determine E (V from battery)Determine E (V from battery) - 12V- 12V
2.2. Find the total Resistance - Find the total Resistance - 6 6 ΩΩ
Finding V, I & R for a Finding V, I & R for a Series CircuitSeries Circuit
1.1. Determine E (V from battery)Determine E (V from battery) - 12V- 12V
2.2. Find the total Resistance Find the total Resistance - - 6 6 ΩΩ
3.3. Determine IDetermine ITT by I by ITT = V = VTT/R/RTT
2 A2 A = 12 V/ 6 = 12 V/ 6 ΩΩ
Finding V, I & R for a Finding V, I & R for a Series CircuitSeries Circuit
1.1. Determine E (V from battery)Determine E (V from battery) - 12V- 12V
2.2. Find the total Resistance Find the total Resistance - - 6 6 ΩΩ
3.3. Determine that IDetermine that IT T = = 2 A2 A
4.4. Since I is constant in a series circuit, find Since I is constant in a series circuit, find V (energy used ) for each resistor using V (energy used ) for each resistor using V = IV = ITTRR
12 V
1 Ω2 Ω
3 Ω
2V2V = 2A * 1 = 2A * 1ΩΩ4V4V = 2A * 2 = 2A * 2ΩΩ
6V6V = 2A * 3 = 2A * 3ΩΩ
1212V = V = 6V6V + + 4V4V + + 2V2V
Series CircuitSeries Circuit• Current is the same at all points Current is the same at all points
I = II = I11 = I = I22 = I = I33 = I = I44
• Volt is divided among all the resistorVolt is divided among all the resistor
E = VE = V11 + V + V22 + V + V33
• Resistance accumulatesResistance accumulates
R = RR = R11 + R + R22 + R + R33
12 V12 V
1 Ω4 Ω
3 Ω
What is the total Resistance?What is the total Resistance?
12 V12 V
1 Ω4 Ω
3 Ω
What is the total Resistance? 8 What is the total Resistance? 8 ΩΩWhat is the current leaving the Battery?What is the current leaving the Battery?
12 V12 V
1 Ω4 Ω
3 Ω
What is the total Resistance? 8 ΩWhat is the total Resistance? 8 Ω
What is the current leaving the Battery? 1.5AWhat is the current leaving the Battery? 1.5A
What is the voltage used by the 1-What is the voltage used by the 1- resistor? resistor?
12 V12 V
1 Ω4 Ω
3 Ω
What is the total Resistance? 8 ΩWhat is the total Resistance? 8 Ω
What is the current leaving the Battery? 1.5AWhat is the current leaving the Battery? 1.5A
What is the voltage used by the 4-What is the voltage used by the 4- resistor? resistor?
12 V12 V
1 Ω4 Ω
3 Ω
What is the total Resistance? 8 ΩWhat is the total Resistance? 8 Ω
What is the current leaving the Battery? 1.5AWhat is the current leaving the Battery? 1.5A
What is the voltage used by the 3-What is the voltage used by the 3- resistor? resistor?
12 V12 V
1 Ω4 Ω
3 Ω
Parallel CircuitParallel Circuit
Finding V, I & R for a Finding V, I & R for a Parallel CircuitParallel Circuit
1.1. Determine EDetermine E2.2. Find the total Resistance Find the total Resistance
1/R1/RT T = 1/R= 1/R11 + 1/R + 1/R2 2 + 1/R+ 1/R33 … …
3.3. Determine IDetermine ITT leaving battery by leaving battery by
IITT = V = VTT/R/RTT
4.4. Since V is constant for each part of a parallel circuit, Since V is constant for each part of a parallel circuit, find I through each resistor using find I through each resistor using
I = V/RI = V/R
5.5. Check to verify that Kirchhoff’s Law is trueCheck to verify that Kirchhoff’s Law is true
1 Ω
2 Ω
12 V
Finding V, I & R for a Finding V, I & R for a Parallel CircuitParallel Circuit
1.1. Determine EDetermine E 12 V12 V
Finding V, I & R for a Finding V, I & R for a Parallel CircuitParallel Circuit
1.1. Determine EDetermine E
2.2. Find the total Resistance Find the total Resistance
1/R1/RT T = 1/R= 1/R11 + 1/R + 1/R2 2 + 1/R+ 1/R33 … …
1 Ω
2 Ω
1/R1/RT T = 1/1= 1/1ΩΩ + 1/2 + 1/2ΩΩ1/R1/RT T = 3/2= 3/2ΩΩ
12 V
RRT T = = 22ΩΩ/3/3
Finding V, I & R for a Finding V, I & R for a Parallel CircuitParallel Circuit
1.1. Determine EDetermine E
2.2. Find the total Resistance Find the total Resistance
1/R1/RT T = 1/R= 1/R11 + 1/R + 1/R2 2 + 1/R+ 1/R33 … …
RRT T = 2= 2ΩΩ/3/3
Finding V, I & R for a Finding V, I & R for a Parallel CircuitParallel Circuit
1.1. Determine EDetermine E
2.2. Find the total Resistance Find the total Resistance
1/R1/RT T = 1/R= 1/R11 + 1/R + 1/R2 2 + 1/R+ 1/R33 … …
3.3. Determine IDetermine IBB leaving battery by leaving battery by
IIBB = V = VBB/R/RTT
IIBB = 12V / 2 = 12V / 2ΩΩ/3 /3 oror 12V x 3/2 12V x 3/2ΩΩ
IIBB = 18A = 18A
1 Ω
2 Ω
12 V
IIBB = 18A = 18A
Finding V, I & R for a Finding V, I & R for a Parallel CircuitParallel Circuit
1.1. Determine EDetermine E
2.2. Find the total Resistance Find the total Resistance
1/R1/RT T = 1/R= 1/R11 + 1/R + 1/R2 2 + 1/R+ 1/R33 … …
3.3. Determine IDetermine ITT leaving battery by leaving battery by
IITT = V = VTT/R/RTT
4.4. Since V is constant for each part of a parallel Since V is constant for each part of a parallel circuit, find I through each resistor using circuit, find I through each resistor using
I = V/RI = V/R
1 Ω
2 Ω
12 V
I = 12V / 1I = 12V / 1Ω = 12AΩ = 12A
I = 12V / 2I = 12V / 2Ω = 6AΩ = 6A
Finding V, I & R for a Finding V, I & R for a Parallel CircuitParallel Circuit
1.1. Determine EDetermine E
2.2. Find the total Resistance Find the total Resistance
1/R1/RT T = 1/R= 1/R11 + 1/R + 1/R2 2 + 1/R+ 1/R33 … …
3.3. Determine IDetermine ITT leaving battery by leaving battery by
IITT = V = VTT/R/RTT
4.4. Since V is constant for each part of a parallel circuit, Since V is constant for each part of a parallel circuit, find I through each resistor using find I through each resistor using
I = V/RI = V/R
5.5. Check to verify that Kirchhoff’s Rule is trueCheck to verify that Kirchhoff’s Rule is true
1 Ω
2 Ω
12 V
18A18A
12A12A
6A6A
18A18A
IIBB = 18A = 18A
Parallel CircuitParallel Circuit
Volt is the same at all points Volt is the same at all points
E = VE = V11 = V = V22 = V = V33
ResistanceResistance 1 1 1 11 1 1 1--- = --- + --- + ------ = --- + --- + --- R RR R11 R R22 R R33
Current accumulatesCurrent accumulates
I = II = I11 + I + I22 + I + I33
2 2 ΩΩ
2 2 ΩΩ
20 V20 V
2 2 ΩΩ2 2 ΩΩ
20 V20 V
What is the voltage?What is the voltage?
2 2 ΩΩ2 2 ΩΩ
20 V20 V
What is the voltage? 20VWhat is the voltage? 20V
What is the total Resistance?What is the total Resistance?
2 2 ΩΩ2 2 ΩΩ
20 V20 V
What is the voltage? 20VWhat is the voltage? 20V
What is the total Resistance? 1.0 ΩWhat is the total Resistance? 1.0 Ω What is the total current?What is the total current?
2 2 ΩΩ2 2 ΩΩ
20 V20 V
What is the voltage? 20VWhat is the voltage? 20VWhat is the total Resistance? 1.0 ΩWhat is the total Resistance? 1.0 Ω
What is the total current? 20 AWhat is the total current? 20 A
What is the voltage through each What is the voltage through each resistor?resistor?
2 2 ΩΩ2 2 ΩΩ
20 V20 V
What is the voltage? 20VWhat is the voltage? 20VWhat is the total Resistance? 1.0 ΩWhat is the total Resistance? 1.0 Ω
What is the total current? 20 AWhat is the total current? 20 AWhat is the voltage through each resistor? 20VWhat is the voltage through each resistor? 20V
What is the current through each What is the current through each resistor?resistor?
2 2 ΩΩ2 2 ΩΩ
20 V20 V
What is the voltage? 20VWhat is the voltage? 20VWhat is the total Resistance? 1.0 ΩWhat is the total Resistance? 1.0 Ω
What is the total current? 20 AWhat is the total current? 20 AWhat is the voltage through each resistor? What is the voltage through each resistor?
20V20VWhat is the current through each resistor?What is the current through each resistor?
10A10A
2 2 ΩΩ
3 3 ΩΩ
24 V24 V
2 2 ΩΩ3 3 ΩΩ
24 V24 V
What is the voltage?What is the voltage?
2 2 ΩΩ3 3 ΩΩ
24 V24 V
What is the voltage? 24VWhat is the voltage? 24V
What is the total Resistance?What is the total Resistance?
2 2 ΩΩ3 3 ΩΩ
24 V24 V
What is the voltage? 24VWhat is the voltage? 24V
What is the total Resistance? 1.2 ΩWhat is the total Resistance? 1.2 Ω What is the total current?What is the total current?
2 2 ΩΩ3 3 ΩΩ
24 V24 V
What is the voltage? 24VWhat is the voltage? 24VWhat is the total Resistance? 1.2 ΩWhat is the total Resistance? 1.2 Ω
What is the total current? 20 AWhat is the total current? 20 A
What is the voltage through each What is the voltage through each resistor?resistor?
2 2 ΩΩ3 3 ΩΩ
24 V24 V
What is the voltage? 24VWhat is the voltage? 24VWhat is the total Resistance? 1.0 ΩWhat is the total Resistance? 1.0 Ω
What is the total current? 20 AWhat is the total current? 20 AWhat is the voltage through each resistor? 24VWhat is the voltage through each resistor? 24V
What is the current through each What is the current through each resistor?resistor?
2 2 ΩΩ3 3 ΩΩ
24 V24 V
What is the voltage? 24VWhat is the voltage? 24VWhat is the total Resistance? 1.0 ΩWhat is the total Resistance? 1.0 Ω
What is the total current? 20 AWhat is the total current? 20 AWhat is the voltage through each resistor? What is the voltage through each resistor?
24V24VWhat is the current through each resistor?What is the current through each resistor?
12A12A + 8A = 20A+ 8A = 20A
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ
What is the voltage?What is the voltage?
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ
What is the voltage? 24VWhat is the voltage? 24V
What is the total Resistance?What is the total Resistance?
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ
What is the voltage? 24VWhat is the voltage? 24V
What is the total Resistance? 1.0 ΩWhat is the total Resistance? 1.0 Ω What is the total current?What is the total current?
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ
What is the voltage? 24VWhat is the voltage? 24VWhat is the total Resistance? 1.0 ΩWhat is the total Resistance? 1.0 Ω
What is the total current? 24 AWhat is the total current? 24 A
What is the voltage through each What is the voltage through each resistor?resistor?
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ
What is the voltage? 24VWhat is the voltage? 24VWhat is the total Resistance? 1.0 ΩWhat is the total Resistance? 1.0 Ω
What is the total current? 24 AWhat is the total current? 24 AWhat is the voltage through each resistor? 24VWhat is the voltage through each resistor? 24V
What is the current through each What is the current through each resistor?resistor?
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ
What is the voltage? 24VWhat is the voltage? 24VWhat is the total Resistance? 1.0 ΩWhat is the total Resistance? 1.0 Ω
What is the total current? 24 AWhat is the total current? 24 AWhat is the voltage through each resistor? What is the voltage through each resistor?
24V24VWhat is the current through each resistor?What is the current through each resistor?
4A + 8A4A + 8A + 12A = 24A+ 12A = 24A
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ
Complex CircuitsComplex Circuits
2 Ω
12 V
2 Ω
2 Ω
Finding V, I & R for a Finding V, I & R for a Complex CircuitComplex Circuit
1.1. Find the most complex portion of the Circuit – usually Find the most complex portion of the Circuit – usually part of the Parallelpart of the Parallel
2.2. Find the Total Resistance for that portionFind the Total Resistance for that portion3.3. Continue until the Total Resistance for the Circuit is Continue until the Total Resistance for the Circuit is
knownknown4.4. Starting with the least complex resistor, find the Starting with the least complex resistor, find the
voltage it usesvoltage it uses5.5. Continue until the parallel portion where the Continue until the parallel portion where the
remaining voltage will used on both sides will be remaining voltage will used on both sides will be identical, Find Iidentical, Find I
6.6. Make sure Kirchhoff's Rule is followedMake sure Kirchhoff's Rule is followed
Finding V, I & R for a Finding V, I & R for a Complex CircuitComplex Circuit
1.1. Find the most complex portion of the Find the most complex portion of the Circuit – usually part of the ParallelCircuit – usually part of the Parallel
2 2 ΩΩ
12 V
2 2 ΩΩ
2 Ω
Finding V, I & R for a Finding V, I & R for a Complex CircuitComplex Circuit
1.1. Find the most complex portion of the Circuit – usually Find the most complex portion of the Circuit – usually part of the Parallelpart of the Parallel
2.2. Find the Total Resistance for that portionFind the Total Resistance for that portion
12 V
2 2 ΩΩ
2 2 ΩΩ
2 Ω
1/R1/RT T = 1/2= 1/2ΩΩ + 1/2 + 1/2ΩΩ1/R1/RT T = 2/2= 2/2ΩΩ
RRT T = 1= 1ΩΩ
1Ω
Finding V, I & R for a Finding V, I & R for a Complex CircuitComplex Circuit
1.1. Find the most complex portion of the Circuit – usually Find the most complex portion of the Circuit – usually part of the Parallelpart of the Parallel
2.2. Find the Total Resistance for that portionFind the Total Resistance for that portion
3.3. Continue until the Total Resistance for the Continue until the Total Resistance for the Circuit is knownCircuit is known
12 V
2 2 ΩΩ
2 2 ΩΩ
2 Ω
RRT T = 2= 2ΩΩ + 1 + 1ΩΩRRT T = 3= 3ΩΩ
1Ω
Finding V, I & R for a Finding V, I & R for a Complex CircuitComplex Circuit
1.1. Find the most complex portion of the Circuit – usually Find the most complex portion of the Circuit – usually part of the Parallelpart of the Parallel
2.2. Find the Total Resistance for that portionFind the Total Resistance for that portion
3.3. Continue until the Total Resistance for the Circuit is Continue until the Total Resistance for the Circuit is knownknown
4.4. Find the Current that leaves the batteryFind the Current that leaves the battery
12 V
2 2 ΩΩ
2 2 ΩΩ
2 Ω
V = IR or I = V/RV = IR or I = V/RI = 12V / 3I = 12V / 3ΩΩ
1Ω
I = 4AI = 4A
, 4A, 4A
Finding V, I & R for a Finding V, I & R for a Complex CircuitComplex Circuit
1.1. Find the most complex portion of the Circuit – usually Find the most complex portion of the Circuit – usually part of the Parallelpart of the Parallel
2.2. Find the Total Resistance for that portionFind the Total Resistance for that portion
3.3. Continue until the Total Resistance for the Circuit is Continue until the Total Resistance for the Circuit is knownknown
4.4. Starting with the least complex resistor, Starting with the least complex resistor, find the voltage it usesfind the voltage it uses
2 2 ΩΩ
12 V, 4A
2 2 ΩΩ
V = IRV = IRSince it is series, I = 4ASince it is series, I = 4A
V = 4A x 2 V = 4A x 2 ΩΩ
V = 8V V = 8V 2 2 ΩΩ8V8V
Finding V, I & R for a Finding V, I & R for a Complex CircuitComplex Circuit
1.1. Find the most complex portion of the Circuit – usually Find the most complex portion of the Circuit – usually part of the Parallelpart of the Parallel
2.2. Find the Total Resistance for that portionFind the Total Resistance for that portion3.3. Continue until the Total Resistance for the Circuit is Continue until the Total Resistance for the Circuit is
knownknown4.4. Starting with the least complex resistor, find the Starting with the least complex resistor, find the
voltage it usesvoltage it uses
5.5. Continue until the parallel portion where Continue until the parallel portion where the remaining voltage will used on both the remaining voltage will used on both sides will be identical, Find Isides will be identical, Find I
12 V, 4A
22Ω Ω
22Ω Ω
2 Ω8V
12V – 8V = 4V12V – 8V = 4V
I = 4V / 2I = 4V / 2Ω = 2AΩ = 2A
I = 4V/2I = 4V/2Ω = 2AΩ = 2A
4V 4V
4V4V
Finding V, I & R for a Finding V, I & R for a Complex CircuitComplex Circuit
1.1. Find the most complex portion of the Circuit – usually Find the most complex portion of the Circuit – usually part of the Parallelpart of the Parallel
2.2. Find the Total Resistance for that portionFind the Total Resistance for that portion3.3. Continue until the Total Resistance for the Circuit is Continue until the Total Resistance for the Circuit is
knownknown4.4. Starting with the least complex resistor, find the Starting with the least complex resistor, find the
voltage it usesvoltage it uses5.5. Continue until the parallel portion where the Continue until the parallel portion where the
remaining voltage will used on both sides will be remaining voltage will used on both sides will be identical, Find Iidentical, Find I
6.6. Make sure Kirchhoff's Rule is followedMake sure Kirchhoff's Rule is followed
12 V, 4A
2 2 Ω, 4VΩ, 4V
2A + 2A = 4A2A + 2A = 4A
2A2A
2A2A
4A4A
4A4A
4A4A
2 Ω8V
2 2 Ω, 4VΩ, 4V
Try this!Try this!
‘Some Electrical Circuit Components and Circuits’ by Michael Condren, Professor of Chemistry, Christian Brothers University, Memphis, TN @ http://www.cbu.edu/~mcondren/chem415/c415_ele.ppt, 4/17/04
R6=5
R1= 5
R2=10
R5=6
R3=6R4=12
Series-Parallel CircuitSeries-Parallel Circuit
R6=5
R1= 5
R2=10R5=6
R3=6R4=12
R7
EXAMPLE: What is the equivalent resistanceand current for the following circuit?
Series-Parallel CircuitSeries-Parallel Circuit
resistors 3 and 4 are in parallelresistors 3 and 4 are in parallel
1 1 1 1 1 1 1 1 1 1 --- = --- + --- = ----- + ---------- = --- + --- = ----- + -------
RR77 R R33 R R44 66 1212
= 0.25= 0.25 -1-1
RR77 = 4 = 4
EXAMPLE: What is the equivalent resistanceand current for the following circuit?
Series-Parallel CircuitSeries-Parallel Circuit
R6=5
R1= 5
R2=10R5=6
R7=4
EXAMPLE: What is the equivalent resistanceand current for the following circuit?
R6=5
R1= 5
R2=10R5=6
R7=4R8
Series-Parallel CircuitSeries-Parallel Circuit
EXAMPLE: What is the equivalent resistanceand current for the following circuit?
Series-Parallel CircuitSeries-Parallel Circuit
resistor 5 and equivalent resistance 7 are in resistor 5 and equivalent resistance 7 are in seriesseries
RR88 = R = R77 + R + R55 = (4 + 6) = (4 + 6) = = 1010
EXAMPLE: What is the equivalent resistanceand current for the following circuit?
Series-Parallel CircuitSeries-Parallel Circuit
R6=5
R1= 5
R2=10 R8=10
EXAMPLE: What is the equivalent resistanceand current for the following circuit?
Series-Parallel CircuitSeries-Parallel Circuit
R6=5
R1= 5
R2=10 R8=10R9
EXAMPLE: What is the equivalent resistanceand current for the following circuit?
Series-Parallel CircuitSeries-Parallel Circuit
resistor 2 and equivalent resistance 8 in resistor 2 and equivalent resistance 8 in parallelparallel
1 1 1 1 11 1 1 1 1--- = ----- + ----- = ------- + ---------- = ----- + ----- = ------- + ------- RR99 R R22 R R88 10 10 1010
= 0= 0.2 .2 -1 -1 ; R ; R9 9 = 5= 5
EXAMPLE: What is the equivalent resistanceand current for the following circuit?
Series-Parallel CircuitSeries-Parallel Circuit
R6=5
R1= 5
R9=5V=7.5v
EXAMPLE: What is the equivalent resistanceand current for the following circuit?
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ3 3 ΩΩ
Try this!Try this!
What is the voltage?What is the voltage?
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ3 3 ΩΩ
What is the voltage? 24VWhat is the voltage? 24V
What is the total Resistance?What is the total Resistance?
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ3 3 ΩΩ
What is the voltage? 24VWhat is the voltage? 24V
What is the total Resistance? 4.0 ΩWhat is the total Resistance? 4.0 Ω What is the total current?What is the total current?
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ3 3 ΩΩ
What is the voltage? 24VWhat is the voltage? 24VWhat is the total Resistance? 4.0 ΩWhat is the total Resistance? 4.0 Ω
What is the total current? 6.0 AWhat is the total current? 6.0 A
What is the voltage through each What is the voltage through each resistor?resistor?
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ3 3 ΩΩ
What is the voltage? 24VWhat is the voltage? 24VWhat is the total Resistance? 4.0 ΩWhat is the total Resistance? 4.0 Ω
What is the total current? 6 AWhat is the total current? 6 AWhat is the voltage through each resistor? What is the voltage through each resistor?
3 Ω: 18V and 6V3 Ω: 18V and 6V
What is the current through each What is the current through each resistor?resistor?
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ3 3 ΩΩ
What is the voltage? 24VWhat is the voltage? 24VWhat is the total Resistance? 4.0 ΩWhat is the total Resistance? 4.0 Ω
What is the total current? 6 AWhat is the total current? 6 AWhat is the voltage through each resistor? What is the voltage through each resistor?
3 Ω: 18V and 6V3 Ω: 18V and 6V What is the current through each resistor?What is the current through each resistor?
3 Ω: 6A and 2 Ω: 3A 3 Ω: 2A 6 Ω: 1A3 Ω: 6A and 2 Ω: 3A 3 Ω: 2A 6 Ω: 1A
3 3 ΩΩ
6 6 ΩΩ
24 V24 V
2 2 ΩΩ3 3 ΩΩ
Power• Power is the amount of energy that is transferred Power is the amount of energy that is transferred
every secondevery second
• Power is measured in wattsPower is measured in watts
P = I x VP = I x V
• PP = The power transferred by the component = The power transferred by the componentII = The current going through a component = The current going through a componentVV = The voltage across a component = The voltage across a component
• Remember that a kilowatt = 1,000 wattsRemember that a kilowatt = 1,000 watts
An electric iron draws a current of An electric iron draws a current of 4A at 250V. What is its power 4A at 250V. What is its power usage?usage?
A.A. 0.0166W 0.0166W
B.B. 60W 60W
C.C. 1000W1000W
A common lightbulb reads 60W, A common lightbulb reads 60W, 120V. How much current in 120V. How much current in amperes will flow through the amperes will flow through the bulb?bulb?
A.A. 7200 amps 7200 amps
B.B. 0.5 amps0.5 amps
C.C. 2.0 amps2.0 amps
PracticePracticeDetermine the cost of using the following appliances for the Determine the cost of using the following appliances for the time indicated if the average cost is 9 cents/kWh.time indicated if the average cost is 9 cents/kWh.
(a) 1200W iron for 2 hours(a) 1200W iron for 2 hours
1.2 kW x (2h) x 9 cents = kWh
12.2 cents
PracticePracticeDetermine the cost of using the following appliances for the time indicated if the average cost is 9 Determine the cost of using the following appliances for the time indicated if the average cost is 9 cents/kWh.cents/kWh.
(a) 1200W iron for 2 hours(a) 1200W iron for 2 hours
(b) 160W color TV for 3 hours and 30 minutes(b) 160W color TV for 3 hours and 30 minutes
1.2 kW x (2h) x 9 cents = kWh
12.2 cents
0.16 kW x (3.5h) x 9 cents = kWh
5.04 cents
PracticePracticeDetermine the cost of using the following appliances for the time indicated if the average cost is 9 cents/kWh.Determine the cost of using the following appliances for the time indicated if the average cost is 9 cents/kWh.
(a) 1200W iron for 2 hours(a) 1200W iron for 2 hours
(b) 160W color TV for 3 hours and 30 minutes(b) 160W color TV for 3 hours and 30 minutes
(c) Six 60W bulbs for 7 hours.(c) Six 60W bulbs for 7 hours.
1.2 kW x (2h) x 9 cents = kWh
12.2 cents
0.16 kW x (3.5h) x 9 cents = kWh
5.04 cents
6 x .06 kW x (7h) x 9 cents = kWh
22.68 cents
Concept TestConcept Test
For resistors in For resistors in seriesseries, what is the same , what is the same for every resistor? R, V or I?for every resistor? R, V or I?
A.A.RR
B.B.VV
C.C.II
Concept TestConcept Test
For resistors in For resistors in parallelparallel, what is the same , what is the same for every resistor? for every resistor?
A.A.RR
B.B.VV
C.C.II
Series-Parallel CircuitSeries-Parallel Circuit
R6=5
R1= 5
R2=10R5=6
R3=6R4=12
EXAMPLE: What is the equivalent resistanceand current for the following circuit?
Bibliography Bibliography 1. ‘Some Electrical Circuit Components and Circuits’ by Michael Condren,
Professor of Chemistry, Christian Brothers University, Memphis, TN @ http://www.cbu.edu/~mcondren/chem415/c415_ele.ppt, 4/17/04
2. ‘Fundamentals of Electronics,’ Dan Bruton, Professor of Astrophysics Stephen F. Austin State University @ observe.phy.sfasu.edu/courses/phy262/ lectures262, 4/17/04