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Circuits
A circuit is a loop of wire with
its ends connected to an
energy source such as a cell*
or a battery*.
One end of the wire is
connected to the positive terminal
The other end of the wire is connected
to the negative terminal. The wire is
connected in this way so a current* can
flow through it.
Series Circuits
• Series circuits are the
simplest type of
circuits.
• Series circuits have all
their parts connected in
one loop of wire.
• On the right is a series
circuit consisting of a
cell and a lamp:
• The series circuit below connects a
cell*, a lamp and an ammeter*.
• The ammeter reads that the current
through the lamp is 1.5 A.
•
• And here is a series
circuit consisting of
a cell and two
lamps:
• Notice that all the
components are
connected in one
loop of wire.
Disadvantages of Series Circuits
• 1st: If one component in a series circuit
fails, then all the components in the
circuit fail because the circuit has been
broken.
2nd: The more components there are in
a series circuit, the greater the circuit's
resistance*.
In the series circuit below, Ammeter 1
shows a reading of 1.5 A.
• What will be the readings on Ammeter 2 and
Ammeter 3?
•
•
•
•
Choose one :
0.5 A and 1.0 A
1.5 A and 1.5 A
1.5 A and 0.0 A
Well done!
• Ammeter 1, Ammeter 2 and Ammeter 3
each show the same reading of 1.5 A.
• A series circuit has just one current.
Parallel Circuits
• A parallel circuit is rather like two or
more series circuits connected to the
same energy source.
• For example, here is a
parallel circuit connecting
a cell* and two lamps:
And here is a parallel circuit
connecting a cell and three
lamps:
Notice that the components lie inside "parallel" loops
connected to the same energy source.
Parallel circuits have two
advantages
• A failure of one component does not
lead to the failure of the other
components.
• More components may be added in
parallel without the need for more
voltage*.
The more components connected in
parallel, the more energy is used.
For example, if each of
the circuits on this page
used the same type of
cell* and same type of
lamp...
...this circuit would light
one lamp for 12 hours:
the circuit below would light two
lamps for 6 hours:
and the circuit below would light three
lamps for 4 hours:
• A cell provides enough energy to light either
a blue lamp or a red lamp for six hours. For
how long will the same cell light both lamps
in parallel?
Choose one answer below:
• 4 hours
• 2 hours
• 3 hours
Well done!
• The cell will light both lamps for 3
hours.
Current in Parallel Circuits
Whereas the current flowing through a
series circuit is the same everywhere,
the current flowing through a parallel
circuit depends upon where in the
circuit the current is measured.
Ammeter 1 reads 1.5 A
flowing through
Lamp 1.
Ammeter 2 also reads
1.5 A as Lamp 2 is
identical to Lamp 1.
Now we connect a third ammeter
next to the cell:
• What current will Ammeter 3 read?
Ammeter 3 reads 3 A
• Ammeter 3 reads 3 A. This is because
the total current* flowing from a cell* in
a parallel circuit equals the sum of all
the currents flowing in the loops.
Ammeters 1, 2, and 3 read 1 A.
Assuming all the lamps are identical,
what will Ammeter 4 read?
Ammeter 3 reads 3 A.
• The total current flowing from a cell in a
parallel circuit equals the sum of all the
currents flowing in the loops.