parts of an electric circuit recall: a circuit is a closed path electric circuit: closed path that...
TRANSCRIPT
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Parts of An Electric Circuit
• Recall: a circuit is a closed path• Electric circuit: closed path that
flowing charge follows• Constructing an electric circuit:• Three key components needed:• “Source”: a source of voltage or
current• Component: a device that
requires electrical energy• Connectors: something to
connect source to component
Images obtained from: http://topdiysolarpanels.com/images/Battery.jpg, http://img6a.flixcart.com/image/coffee-maker/g/9/f/philips-hd7450-hd-7450-400x400-imadbgg73hcavgem.jpeg, http://upload.wikimedia.org/wikipedia/commons/e/e2/Jumper_Wires_with_Crocodile_Clips.jpg
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Circuit Diagrams
• Circuit diagram: standardized method of illustrating the parts of a circuit• Components, sources have
specific symbols• Many components– what we’ll
use is the tip of the iceberg
Image obtained from: http://4.bp.blogspot.com/-ECAHR2CPhuk/VCIN8cSmS6I/AAAAAAAAABA/83QAT5nuZAI/s1600/100W%2BLM3886%2BParallel%2BStereo%2BPower%2BAmplifier.png
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Circuit Sources
• Battery• Provides potential difference for
circuit• Electrons will flow from high
voltage to low voltage in circuit
Positive end
Negative end
+
-
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Circuit Components
• Switch• Controls path of current
within circuit• On: ends of switch
connected, closes circuit• Off: ends of switch not
connected, circuit open
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Circuit Components
• Resistor• Creates resistance in circuit• Serve to reduce amount of
voltage remaining in circuit• Causes energy to be released
from it– often thermal energy• Example: incandescent light
bulb
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Circuit Components
• Rheostat/Potentiometer• Variable resistor: can change
its resistance
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As You Come In…
• Find the voltage drop in this part of a circuit:
5.0 Ω
0.15 A
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Circuit Components
• Capacitor• Stores charge in the circuit• Acts like temporary battery• Builds up charge when
connected to source until full• Discharges charge when
disconnected from source until empty
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Circuit Components
• Inductor• Resists changes in current• If connected to source,
keeps current from flowing for a while• If disconnected from
source, keeps current flowing for a while (how???)
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Circuit Components
• Ammeter• Measures current running
through part of circuit
A
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Circuit Components
• Voltmeter• Measures voltage running
through part of circuit
V
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Circuit Components
• Generic Device• Appliance or general
electrical device that is part of circuit Name
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Circuit Connectors
• Conductor/wire• Connects sources, components• Assumed to have negligible
resistance• Junctions• Sometimes connectors cross
paths or intersect• Node: conductors connect• No node: conductors do not
connect
Node
No node
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Circuit Connectors
• Ground• Connects circuit to “ground”• “Ground” has electrical potential
of 0 V• Prevents short circuits– more on
those later!
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Circuit Diagrams: Determining Current• Given the following circuit diagram:• Want to know I• Magnitude of I is simple: R = V / I I = V / R• What about direction?Electron flow notation: electrons flow from (-) to (+) of a voltage sourceCurrent flowing CCW
3.0
Ω
1.5 V
⨡⨡
-+
I = 0.50 A
= 0.50 A
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Circuit Diagrams: Series Circuits
• Given the following circuit diagram:• Resistors are in a series– one after
another along one path• Called a “series circuit”
R 2 = 3
.0 Ω
1.5 VR1 = 5.0 Ω
R3 = 1.0 Ω
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Circuit Diagrams: Series Circuits
• What do we know about circuit?• Only one path for electrons to
flow• Current through each resistor
must be the same• I1 = I2 = I3
• Voltage drop by end of path must equal voltage of source• V1 + V2 + V3 = Vtotal
R 2 = 3
.0 Ω
1.5 VR1 = 5.0 Ω
R3 = 1.0 Ω
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Circuit Diagrams: Series Circuits
• Resistors in Series:• I1 = I2 = I3
• V1 + V2 + V3 = Vtotal
• Since all the currents are the same, can rewrite above as:
• Because R = , this simplifies to R1 + R2 + R3 = Rtotal
R 2 = 3
.0 Ω
1.5 VR1 = 5.0 Ω
R3 = 1.0 Ω
= I
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Circuit Diagrams: Series Circuits
• Resistors in Series:• I1 = I2 = I3
• V1 + V2 + V3 = Vtotal
• Since all the currents are the same, can rewrite above as:
• Because R = , this simplifies to R1 + R2 + R3 = Rtotal
R tota
l = 9
.0 Ω
1.5 V
Equivalent Circuit
= I
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Circuit Diagrams: Series Circuits
• Resistors in Series:• I1 = I2 = I3
• V1 + V2 + V3 = Vtotal
• Since all the currents are the same, can rewrite above as:
• Because R = , this simplifies to R1 + R2 + R3 = Rtotal
R tota
l = 9
.0 Ω
1.5 V
Equivalent Circuit
= I
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Practice Problem: Series Circuit
• Given the following circuit diagram, what is the resistance of R2?• R1 + R2 = Rtotal
• Rtotal = • 1.5 Ω + R2 = 2.0 Ω So R2 = 0.5 ΩR 2 =
?6.0 V
R1 = 1.5 Ω
3.0 A
= = 2.0 Ω
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About Series Circuits
• Advantages:• Easy to set up (cheap)• Batteries in series: voltages additive,
increases current• Less connectors needed
• Disadvantages:• Voltage divided between components–
more components, less voltage for each• One path for current– if one component
fails, circuit fails• Resistance increases– decreases current
within circuit
R 2 = 3
.0 Ω
1.5 VR1 = 5.0 Ω
R3 = 1.0 Ω
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Circuit Diagrams: Parallel Circuits
• Given the following circuit diagram:• Resistors along multiple, different,
parallel paths• Called a “parallel circuit”
1.5 V
R1 = 5.0 Ω
R2 = 3.0 Ω
R3 = 1.0 Ω
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Circuit Diagrams: Parallel Circuits
• What do we know about circuit?• Multiple paths for e- to flow• Total current of circuit equal to
current through each resistor• I1 + I2 + I3 = Itotal
• Voltage drop the same across each resistor– equals voltage of source• V1 = V2 = V3 = Vtotal
1.5 V
R1 = 5.0 Ω
R2 = 3.0 Ω
R3 = 1.0 Ω
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Circuit Diagrams: Parallel Circuits
• Resistors in Parallel:• V1 = V2 = V3
• I1 + I2 + I3 = Itotal
• Since all the voltages are thesame, can rewrite above as:
• Since R = , that means = ; thus,
1.5 V
R1 = 5.0 Ω
R2 = 3.0 Ω
R3 = 1.0 Ω
= V
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Circuit Diagrams: Parallel Circuits
• Resistors in Parallel:• V1 = V2 = V3
• I1 + I2 + I3 = Itotal
• Since all the voltages are thesame, can rewrite above as:
• Since R = , that means = ; thus,
1.5 V Rtotal = 1.8 Ω
Equivalent Circuit
= V
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Practice Problem: Parallel Circuit
6.0 V
R1 = 15 Ω
R2 = 5.0 Ω
R3 = 7.5 Ω
• Given the following circuit diagram, what would be the reading on the ammeter?
• 0.067 + 0.20 + 0.13 = = 0.40 , therefore R = 2.5 Ω• I = V / Rtotal
???
= 6.0 V / 2.5 Ω = 2.4 A
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About Parallel Circuits
1.5 V
R1 = 5.0 Ω
R2 = 3.0 Ω
R3 = 1.0 Ω
• Advantages:• Voltage the same across each component• Total resistance decreases compared to
each component’s resistance• Batteries in parallel make batteries last
longer• Multiple paths for current– can be
redirected if one part of circuit fails
• Disadvantages:• More connectors needed• Batteries in parallel do not add to the
voltage of the circuit
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Circuit Diagrams: More About Series Circuits
• Capacitors in Series:• Recall: V1 + V2 + V3 = Vtotal for series
circuit• Capacitors in series act like one big
capacitor
C 2 = 0
.8 F
1.5 VC1 = 1.2 F
C3 = 0.4 F
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Circuit Diagrams: More About Series Circuits
• Capacitors in Series:• Recall: V1 + V2 + V3 = Vtotal for series
circuit• Capacitors in series act like one big
capacitor– one amount of charge (Q)
• Since C = , that means = ; thus,
C tota
l = ?
??1.5 V
Equivalent Circuit
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Circuit Diagrams: More About Series Circuits
• Capacitors in Series:• Recall: V1 + V2 + V3 = Vtotal for series
circuit• Capacitors in series act like one big
capacitor– one amount of charge (Q)
• Since C = , that means = ; thus,
C tota
l = 0
.2 F
1.5 V
Equivalent Circuit
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Circuit Diagrams: More About Parallel Circuits• Capacitors in Parallel:• Recall: V1 = V2 = V3 = V for parallel
circuit• Capacitors in parallel are
independent of one another– each contain their own charge• Q1 + Q2 + Q3 = Qtotal
• Because C = , this simplifies to• C1 + C2 + C3 = Ctotal
1.5 V
C1 = 1.2 F
C2 = 0.8 F
C3 = 0.4 F
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Circuit Diagrams: More About Parallel Circuits• Capacitors in Parallel:• Recall: V1 = V2 = V3 = V for parallel
circuit• Capacitors in parallel are
independent of one another– each contain their own charge• Q1 + Q2 + Q3 = Qtotal
• Because C = , this simplifies to• C1 + C2 + C3 = Ctotal
1.5 V Ctotal = 2.4 F
Equivalent Circuit
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Circuits in Both Series and Parallel
• Many circuits utilize both series and parallel circuit properties within a circuit• Case in point:• How do you find the
equivalent resistance of this circuit?• Recommend: drawing
equivalent circuits
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Equivalent Circuits
• Strategy: equivalent circuits• Pick out parts that are
exclusively in series or in parallel• Simplify that part of circuit• Repeat as needed until only
one equivalent circuit component remains• Question: What part should
be simplified first for this problem?
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Equivalent Circuits
• Step 1: Parallel Circuit
• R = = 0.5
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Equivalent Circuits
• Step 1: Parallel Circuit
• R = = 0.5 • So what’s the next step?
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Equivalent Circuits
• Step 2: Series Circuit• R1 + Reqv + R5 = Rtotal
• 1.0 Ω + 0.5 Ω + 3.5 Ω = Rtotal
• 5.0 Ω = Rtotal
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Equivalent Circuits
• Step 2: Series Circuit• R1 + Reqv + R5 = Rtotal
• 1.0 Ω + 0.5 Ω + 3.5 Ω = Rtotal
• 5.0 Ω = Rtotal
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Equivalent Circuits
• Try this one on your own!
Step 1Step 2
Step 3
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As You Come In…
• How should a voltmeter be inserted into a circuit?
• How should an ammeter be inserted into a circuit?
VParallel: V equal for both branches
Very high R so very little current comes through
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As You Come In…
• How should a voltmeter be inserted into a circuit?
• How should an ammeter be inserted into a circuit?
VParallel: V equal for both branches
Very high R so very little current comes through
ASeries: I equal since along same path
Very small R so very little voltage lost to device