agenda today –finish chapter 25 –cover resistors in dc circuits tues lab & quiz on ch. 24-25...
TRANSCRIPT
Agenda
• Today– Finish Chapter 25– Cover Resistors in DC circuits
• Tues Lab & Quiz on Ch. 24-25
• Finish 26 this week then….– Freedom?
CircuitCurrent made up of “+” charges
Call them “holes”
R1I
+
-
“+” charges s exit + terminalFlow through circuitReturn to “-” terminalNeed return path for current flow
CircuitCurrent made up of “+” charges
Call them “holes”
R1I
+
-
“+” charges s exit + terminalFlow through circuitReturn to “-” terminalNeed return path for current flowWhat happens here?
- +
CircuitCurrent made up of “+” charges
Call them “holes”
R1I
+
-
“+” charges s exit + terminalFlow through circuitReturn to “-” terminalCall “-” zero volts as reference here
0 V
Indicates “ground” reference
Voltage in a given area
R1I
+
-
0 V
A
B
C
DE
FA B
Distance
V
0
1.5V
Voltage in a given area
R1I
+
-
0 V
A
B
C
DE
FA B
Distance
V
0
1.5V
Voltage Constant in a wire!
Voltage in a given area
R1I
+
-
0 V
A
B
C
DE
FB C
Distance
V
0
1.5V
Voltage in resistor?
Voltage in a given area
R1I
+
-
0 V
A
B
C
DE
FB C
Distance
V
0
1.5V
Voltage in resistor?Not constant: Why linear? Resistance increases with length…. R=L/A
Voltage in a given area
R1I
+
-
0 V
A
B
C
DE
FC D
Distance
V
0
1.5V
Voltage in ?
Voltage in a given area
R1I
+
-
0 V
A
B
C
DE
FC D
Distance
V
0
1.5V
Voltage in ?Wire: ~ constant
Voltage in a given area
R1I
+
-
0 V
A
B
C
DE
FC E
Distance
V
0
1.5V
Voltage in ?Wire: ~ constant
D
Voltage in a given area
R1I
+
-
0 V
A
B
C
DE
FC E
Distance
V
0
1.5V
Voltage in ?Wire: ~ constant
D F
Voltage in a given area
R1I
+
-
0 V
A
B
C
DE
FF A
Distance
V
0
1.5V
Voltage in Battery?Voltage Source?
Voltage in a given area
R1I
+
-
0 V
A
B
C
DE
FF A
Distance
V
0
1.5V
Voltage in increases from “-” to “+”Nor clear internal workingsNo matter, just worry about terminal areas
Voltage in a given area
R1I
+
-
0 V
A
B
C
DE
FA B
Distance
V
0
1.5V
Complete CircuitVoltage ends where it began… (Loop)
C F A
Voltage Loop Math
I
+
-
0 V
A
B
C
DE
F
VA – VA = 0VAA = VA – VA
VAB = VA – VB VAA = VAB + VBC + VCD + VDE + VEF + VFA = 0VAA = 0 + 1.5V + 0V + 0 V + 0V + (-1.5V) = 0Useful trickFind any loop in a circuitVoltage around entire loop must be zeroPowerful….
1.5 V Battery
Back to Energy
• Power = Watts (W)
• Power = J/s [Energy per second]
• Volts = J/C
• Energy = V x C
• Power = Energy / time = V x C/s
• Power = IV
Electricity Equations
• Big 2!
• V = IR
• P = IV
• Mix & Match
• P=I2R, P=V2/r, etc…
Energy Conservation
• Energy in = Energy Out
• Power in = Power Out
I
+
-
0 V
A
B
E
F
Power into Circuit: From BatteryPower Out of Circuit: ResistorR’s Convert Electricity to Heat, light, etc,,,Toaster?
Charge Conservation
• Charge in = Charge Out
• Current in = Current Out
I
+
-
0 V
A
B
E
F
Current into Circuit: From BatteryCurrent flowing through : Resistor, Wires IBAT = IWIRE = IR
No other way to go!
Resistor Combinations
• Wish to discover “total” or equivalent resistance for a combination of multiple Resistors
• Most circuits have >1 component…• Insight into output of power source• Useful first step in determining circuit properties• Resistors useful
– Control V & I– Create light & heat– Protection of sensitive components
• Examine logic, conservation laws, math, observations
Water tower
Water TowerPotential Energy from Gravity
PE = mghForces water down [pressure]
Which Allows the most water to flow per minute?
A:Both Connected
Water tower
Water TowerPotential Energy from Gravity
PE = mghForces water down [pressure]
Which Allows the most water to flow per minute?
B:Only Left Connected
Water tower
Water TowerPotential Energy from Gravity
PE = mghForces water down [pressure]
Which Allows the most water to flow per minute?
C:Only Right Connected
Water tower
Water TowerPotential Energy from Gravity
PE = mghForces water down [pressure]
Which Allows the most water to flow per minute?Addition of multiple hoses to same starting point increases flow & Decreases Resistance
A:Both Connected
Water tower
Water TowerPotential Energy from Gravity
PE = mghForces water down [pressure]
Addition of multiple hoses to same starting point increases flow & Decreases ResistanceWhat if we added a third? Fat or skinny? Would flow ever decrease?
A:Both Connected
Water tower
Water TowerPotential Energy from Gravity
PE = mghForces water down [pressure]
Rule one of hoses (& resistors):Multiple pathways reduce resistance“Parallel” Connections
Water tower
Water TowerPotential Energy from Gravity
PE = mghForces water down [pressure]
Compare PE for water falling through the two hoses…Same for bothExamine electrical circuit
Parallel Circuit
I +
-
AB
E
C
F G
Top of Tower
Drain
Compare Voltages at A,B,C
Parallel Circuit
I +
-
AB
E
C
F G
Top of Tower
Drain
Compare Voltages at E,F,G
Parallel Circuit
I +
-
AB
E
C
F G
Top of Tower
Drain
Compare Voltages across Battery & R’sDoes the size of each R matter?
Parallel Circuit
I +
-
AB
E
C
F G
Top of Tower
Drain
Compare Voltages across Battery & R’sDoes the current have to be the same?
Parallel Circuit
I +
-
AB
E
C
F G
Top of Tower
Drain
Compare Voltages across Battery & R’sDoes the current have to be the same?
Parallel Circuit Rules
• Voltage same across parallel components
• Current Can be Different
• Each additional component reduces total resistance
• Derive this for three resistors?– Turn in for extra credit on quiz tomorrow…
Water towerWater Tower
Which Allows the most water to flow per minute?
A:Both Connected
Water towerWater Tower
Which Allows the most water to flow per minute?
B:Thick one?
Water towerWater Tower
Which Allows the most water to flow per minute?
C:Just Skinny?
Water towerWater Tower
Which Allows the least water to flow per minute?
A:Both Connected
Water towerWater Tower
Addition of multiple hoses in line decreases flow & Iecreases ResistanceWhat if we added a third? Fat or skinny? Would flow ever increase?
Water towerWater Tower
Another Rule of hoses: (resistors?)Addition of more hoses in line (“Series”) always Increases resistance
Water tower
Water Tower
Compare flow of water through each pipe…Same for both: What leaves one must enter the other….Examine electrical circuit
Series Circuit
I +
-
AB
D C
Top of Tower
Drain
Compare Voltages at A,B,C, D
E
R1
R2
Series Circuit
I +
-
AB
D C
Top of Tower
Drain
Compare Voltages across R1 & R2 vs. Battery
E
R1
R2
Series Circuit
I +
-
AB
D C
Top of Tower
Drain
Compare Current from Battery & through R’s
R1
R2
E
Series Circuit Rules
• Current same along components in series
• Voltage Can be Different
• Each additional component increases total resistance
• Derive this for three resistors?– Turn in for extra credit on quiz tomorrow…
Parallel Circuit Rules
• Voltage same across parallel components
• Current Can be Different
• Each additional component reduces total resistance
• Derive this for three resistors?– Turn in for extra credit on quiz tomorrow…
Agenda
• Today– Finish Chapter 25
• Monday– Simple Circuitry (ch. 26)
• Tues Lab & Quiz on Ch. 24-25• Wed: Solve Resistor Circuits• Fri: Capacitors in DC circuits….
– Freedom?
• Summer / Other Res. Interest…