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Equivalent Resistance. Series and Parallel Circuits. Two Kinds of circuits. Circuit Diagrams. When drawing pictures of circuits, symbols are used as shorthand instead of pictures of components. Circuit Diagrams. Instead of a battery, the symbol - PowerPoint PPT Presentation
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Equivalent Resistance
Series and Parallel Circuits
Two Kinds of circuits
Circuit Diagrams
• When drawing pictures of circuits, symbols are used as shorthand instead of pictures of components.
Circuit Diagrams
• Instead of a battery, the symbol is used. (Note: sometimes voltage is called emf or
potential difference)
Circuit Diagrams
• Instead of a resistor, the symbol is used.
Circuit Diagrams
• Resistors and batteries will be labeled with their respective values most of the time.
9V
10 Ω
10 Ω
Practice
• Draw a series circuit with a 5V battery and two resistors (one 3Ω and the other 5Ω)
Practice
• Draw a series circuit with a 5V battery and two resistors (one 3Ω and the other 5Ω)
5V
3 Ω
5 Ω
Practice
• Draw a parallel circuit with a 12V battery and two resistors (one 6Ω and the other 2Ω)
Practice
• Draw a parallel circuit with a 12V battery and two resistors (one 6Ω and the other 2Ω)
12V
6 Ω 2 Ω
Using Ohm’s Law (V=IR)
• Ohm’s Law can be applied to
A) the WHOLE circuitor
B) each RESISTOR separately
Ohm’s Law- WHOLE Circuit
• What is Rtotal for the circuit? What is the current?
5V
3 Ω
5 Ω
Ohm’s Law- WHOLE Circuit
• Rtotal:
• I:
5V
3 Ω
5 Ω
85321 RRRtotal
AV
I
IVIRV
6.08
5
)8(5
Ohm’s Law- EACH Resistor
• What is the voltage in each resistor?
5V
3 Ω
5 Ω
Ohm’s Law- EACH Resistor
• What do we know about the current in each resistor?
5V
3 Ω
5 Ω
Ohm’s Law- EACH Resistor
• What do we know about the current in each resistor?
5V
3 Ω
5 Ω
21 IIItotal
Ohm’s Law- EACH Resistor
• With that in mind we can solve for voltage.3Ω resistor 5Ωresistor
5V
3 Ω
5 Ω
Ohm’s Law- EACH Resistor
• With that in mind we can solve for voltage.3Ω resistor 5Ωresistor
5V
3 Ω
5 Ω
VV
AV
IRV
8.1
)3)(6.0(
Ohm’s Law- EACH Resistor
• With that in mind we can solve for voltage.3Ω resistor 5Ωresistor
5V
3 Ω
5 Ω
VV
AV
IRV
8.1
)3)(6.0(
VV
AV
IRV
0.3
)5)(6.0(
Ohm’s Law- EACH Resistor
• Double check your answer to be sure.3Ω resistor 5Ωresistor
5V
3 Ω
5 Ω
VV
AV
IRV
8.1
)3)(6.0(
VV
AV
IRV
0.3
)5)(6.0(
VV 0.38.1
Summary- SERIES Circuits
• We can write the ways we used Ohm’s Law as:
...
...
...
321
321
321
RRRR
IIII
VVVV
total
total
total
Whole Resistor 1, Resistor 2, Resistor3, …Circuit
Practice
• Pg. 650 Practice A
Ohm’s Law for PARALLEL circuits
PARALLEL (WHOLE circuit)
• To apply Ohm’s Law (V=IR) to the WHOLE circuit:
V=10V
10V
2 Ω 4 Ω
PARALLEL (WHOLE circuit)
• To apply Ohm’s Law (V=IR) to the WHOLE circuit:
V=10V
10V
2 Ω 4 Ω
33.175.
1
75.01
4
1
2
1111
21
total
total
total
R
R
RRR
PARALLEL (WHOLE circuit)
• To apply Ohm’s Law (V=IR) to the WHOLE circuit:
V=10V Rtotal=1.33Ω I=?
10V
2 Ω 4 Ω
PARALLEL (WHOLE circuit)
• To apply Ohm’s Law (V=IR) to the WHOLE circuit:
V=10V Rtotal=1.33Ω I=?
V=IR → 10V=I(1.33Ω)
10V
2 Ω 4 Ω
PARALLEL (WHOLE circuit)
• To apply Ohm’s Law (V=IR) to the WHOLE circuit:
V=10V Rtotal=1.33Ω I=7.51A
10V
2 Ω 4 Ω
PARALLEL (EACH resistor)
• Now find the CURRENT in each resistor.
10V
2 Ω 4 Ω
PARALLEL (EACH resistor)
• What do we know about VOLTAGE in a PARALLEL circuit?
10V
2 Ω 4 Ω
PARALLEL (EACH resistor)
• The VOLTAGE is the same everywhere…
10V
2 Ω 4 Ω
V= 10Volts everywhere…
PARALLEL (EACH resistor)
• Now use V=IR to solve for current at each resistor:
2Ω resistor 4Ω resistor
10V
2 Ω 4 ΩV= 10V V= 10V
IA
IV
IRV
5
)2(10
IA
IV
IRV
5.2
)4(10
PARALLEL (EACH resistor)
Total Circuit: V=10V Rtotal=1.33Ω I=7.51A
Compare the currents2Ω resistor 4Ω resistor
10V
2 Ω 4 ΩV= 10V V= 10V
IA
IV
IRV
5
)2(10
IA
IV
IRV
5.2
)4(10
Equal
+
Summary of Ohm’s Law
• For PARALLEL circuits:
• Vtotal=V1=V2=V3=…
• Itotal=I1+I2+I3+…
• ...1111
321
RRRRtotal
10V
2 Ω 4 Ω
Practice
• Find• A) total resistance in circuit• B) current in each resistor
12V
6 Ω 2 Ω