Chapter 6
Series-Parallel Circuits
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Examples of Series-Parallel Circuits
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Basic Configurations
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An Example for Analysis:
Series Circuits Connected in Parallel
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Team Activity: Problem 1 on
p. 173 – Method 1
• Use the voltage divider
method to calculate the
voltages across R1 & R2.
• Use the voltage divider
method to calculate the
voltages across R3 & R4.
• Calculate the current
through R1 & R2.
• Calculate the current
through R3 & R4.
• Calculate the total current
IT.
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Team Activity: Problem 1 on
p. 173 – Method 2
• Find the equivalent resistances R12 & R34.
• Find the total resistance RT.
• Find the total current IT.
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A Second Example:
Parallel Circuits Connected in Series
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Team Activity: Problem 5 on
p. 174.
• Find the equivalent resistances R12 & R34.
• Calculate the total current IT.
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Wheatstone Bridge
Galvanometer – a sensitive ammeter
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• Bridge Operation – based on three
possible states:
VA = VB VA > VB VA < VB
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Wheatstone Bridge:
A series-parallel arrangement at
“balance”
• Resistors R1 and R2 are in
series
– R12 = R1 + R2
• Resistors R3 and R4 are in
series
– R34 = R3 + R4
• Equivalent resistance R12
is in parallel with equivalent
resistance R34
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Circuit Analysis at “balance”,
galvanometer current =0
R
V V
R R
R
V V
R R
V V
2
A
S
1
2
4
B
S
3
A
4
B
R
R

R R
R R
R
R

R
R
2
1
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2
3
2
4
1
3
4
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Application of a Wheatstone Bridge:
Smoke Detector
Photoconductive Cells – Light-Controlled Resistors Used
as Sensor and Reference
When the amount of light striking the device increases,
the resistance decreases (and vice-versa).
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Detector Diagram
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How it works
When the air is clear,
the bridge is balanced.
If smoke enters the
lower chamber via the
vents, the resistance
of the lower
photoconductive cell
increases, causing the
bridge to become
unbalanced, triggering
the alarm.
SMOKE
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