Series and Parallel Circuits
Circuits
In order for electricity to flow we need
Power source
Closed circuit
There are two type of circuits we will
explore
Series circuit
Parallel circuit
Series Circuit
In a series circuit there is only one path for
the electrons to flow
In other words all the components are in
series with each other
Because there is only one path each
charge will go through each resistor
Predict, Test and Explain
• How will the brightness of the bulbs change
as we add more in series?
+
+
+
• What does this imply about the current in the
circuit?
Parallel Circuit
In a Parallel circuit there are multiple pathways for
charge to flow
Each device is placed on it’s own separate branch
Current goes through each of the branches at the same
time
Predict, Test and Explain
• How will the brightness of the bulbs change
as we add more in parallel?
+
+
+
• What does this imply about the current in the
circuit?
Key Concepts
Bulbs in series represent a source of
resistance to current flow, similar to
boulders in a stream which can block
the flow of water
Bulbs in parallel offer additional
pathways for current flow, similar to
branches of a stream which can carry
more water.
Calculating Resistance in Series
Circuits
The rule for
calculating Series
Circuits is to…
Add up the values of
each individual in the
series.
R1 + R2 + R3…
5 + 5 + 10
20 Ω (ohms)
Calculating Resistance in Series
Circuits
Add up the values of
each individual in the
series.
R1 + R2 + R3…
10 + 20 + 10
40 Ω (ohms)
10
20
Calculating Resistance in Series
Circuits
 The rule for calculating Series
Circuits is to…
 Add up the values of each
individual in the series.
 1 1
1
1
-- = -- + -- + - 1
Rt R1 R2 R3
-- = 1
 1 1 1 1
Rt
-- = -- + -- + -Rt 4 4 2
 1
-- = Rt
 1
1
-- = .25 + .25 + .5
Rt
 Rt = 1 Ω (ohms)
 1
-- = 1
Rt
 1
-- = 1
Rt
20
•
•
•
•
•
•
•
Calculating Resistance in Series
Circuits
The rule for calculating Series
Circuits is to…
Add up the values of each
individual in the series.
1 1
1
1
-- = -- + -- + -• 1
Rt R1 R2 R3
-- = Rt
1 1
1
1
.016
-- = -- + -+ -Rt 100 200 1000
• Rt = 62.5 Ω
(ohms)
1
-- = .01 + .005 + .001
Rt
1
-- = .016
Rt
1
-- = .016
Rt
100
200
1000
20