Download Series and Parallel Circuits

1 of 9
© Boardworks Ltd 2009
Series and parallel circuits
Circuit components can be wired in series or parallel.
A series circuit has all its
components wired in the
same loop.
These tree lights are
wired in series.
A parallel circuit contains
junctions, and so there is more
than one path for the current.
Car headlights are wired in
parallel. What would happen
if they were wired in series?
2 of 9
© Boardworks Ltd 2009
Series circuits – experiment
3 of 9
© Boardworks Ltd 2009
Current in a series circuit
In a series circuit, the current flows through one continuous
pathway.
So, the current is the same in all parts of a series circuit.
1A A
A
1A
A
1A
4 of 9
© Boardworks Ltd 2009
Voltage in a series circuit
In a series circuit, the voltage supplied by the battery is
shared by the components. So, the sum of the potential
difference across the components equals the battery voltage.
V
V
3V
6V
V
3V
As more bulbs are added in series, each bulb has less
potential difference, and so the bulbs become dimmer.
5 of 9
© Boardworks Ltd 2009
Resistance in a series circuit
In a series circuit, the total resistance is the sum of the
resistance of each component. How the voltage gets shared
depends on the resistance of each component.
V
R=2W
6V
R=4W
V=4V
V = 2V
Total resistance is 6 W and the voltage is 6 V. Each
component gets 1 A of current, but they get different
voltage, because they have different resistances.
6 of 9
© Boardworks Ltd 2009
Parallel circuits – experiment
7 of 9
© Boardworks Ltd 2009
Current in a parallel circuit
In a parallel circuit, the current divides at the point where the
circuit branches and then recombines to complete the circuit.
So, the current is not the same in all parts of a parallel circuit.
A 2A
2A A
1A
A
A
1A
8 of 9
© Boardworks Ltd 2009
Potential difference in parallel circuits
In a parallel circuit, the
potential difference across
each bulb is the same as
the potential difference
across the battery.
V
This means that all the
bulbs have the same
brightness, and they are
brighter than the same
number of bulbs in a
series circuit.
V
However, this also means that
the battery will run down
faster in a parallel circuit.
V
9 of 9
6V
6V
6V
© Boardworks Ltd 2009
Total Resistance in parallel circuits
In a parallel circuit, the total
resistance is LESS than the
sum of the components’
resistance
The total resistance is the
reciprocal of the sum of
the components
resistance:
1/Rtotal = 1/R1 + 1/R2 + 1/R3
….
Rtotal = 1.333 W
6V
Itotal = 4.5 A
R=2W
I=3A
I = 1.5 A
R=4W
10 of 9
© Boardworks Ltd 2009
11 of 9
© Boardworks Ltd 2009
Circuit Pyramids
#2 Ohms Law
V
(V)
I
(A)
#3 Electrical Power
P
(w)
Capital Greek
Omega
R
(W)
V
(V)
I
(A)
Power also =
(I)(R)(I) = I2R
12 of 5
© Boardworks Ltd 2009
Comparing circuits
13 of 9
© Boardworks Ltd 2009