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A circuit is like a central heating
system in a house:
low pressure
Boiler
and
pump
radiator
flow of
water
There is a pump that
High pressure pushes water round
the system. The water
everywhere starts to
move AT THE SAME
TIME.
There are pipes that
CARRY the water.
In the pipes the water
is FLOWING.
© Boardworks Ltd 2003
An electrical circuit is very similar to a
central heating system.
The __ __ in the circuit is like a radiator. An electrical
device uses electrical energy supplied by the circuit.
Instead of a flow
of water, electricity
flows in an
electrical circuit.
The _______ are
like pipes; they
carry the
electricity
(called current)
round the circuit.
The electrical current is pushed by the _______, which has the
same function as the pump and boiler.
The strength of push provided by the battery is called its voltage.
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Series circuit
This is a simple series circuit. In a simple
series circuit, everything is connected in one
loop across the terminals of the battery. So
there AREN’T any points where the current can
split or join (these are called junctions).
This circuit has two lamps connected in series.
Circuits are always drawn using straight lines.
lamps
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Parallel circuits
A
B
A parallel circuit is one which contains a point (a
junction) where the current can SPLIT (point A) or
JOIN (point B). This means that there is MORE than
one path around the circuit.
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Series circuit
Here are some other simple series circuits:
1. Two resistances (resistors) connected in series.
R1
R2
2. A rheostat (or variable resistor) and a bulb connected in series.
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Measuring voltage - across a resistance or
a bulb
A
Components
component
here
R
V
Voltage is measured by connecting the voltmeter V across
(or in parallel with) the component.
Voltage is measured in volts and the symbol for this is V.
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Circuit 1
V
Circuit2
Circuit2
V
R1
R1
R2
V
V1
V2
The _______ is the amount of push.
When two components were put into Circuit 2, the voltage
of the supply was the ____ as Circuit 1. However, the
voltage across R1 ________ .
The voltage across both components in circuit 2 added to
be equal to the _____ voltage.
supply, decreased, voltage, flow, same
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REMEMBER:
The voltage supplied by the battery is shared
between all the components in a series circuit.
V(supply) = V1 + V2
The voltage supplied by the battery is
stays the same for all the components
in a parallel circuit.
V(supply) = V1 = V2 = V3
© Boardworks Ltd 2003
Measuring current
The unit of measure for current is the "amp" which
has the symbol A.
We measure the current using a device called an
ammeter. In a circuit this is given the symbol A
When measuring the current through a
component, the ammeter is always connected in
series (in the same loop) with that component.
A
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Experiment: measuring current
Circuit 1
1
A
R1
A
2
1. Set up the circuit as shown above.
2. Measure the current using the ammeter at positions
1 and 2.
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Experiment: measuring current
Circuit 2
1
A
A
R1
A
3
R2
2
1. Add another resistor into the circuit.
2. Now measure the current using the ammeter at
positions 1, 2 and 3.
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Conclusions
Circuit 1
The current at different positions in the circuit, before and
after the resistor, was the _____.
Current is ___ used up by the components in the circuit.
Circuit 2
Increasing the number of components in the circuit
_______ the current.
The current at all points in a series circuit is the ____.
same / same / decreased / not
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Measuring current in parallel circuits
1
A1
A2
2
A4
4
A3
3
Ammeter
A1
A2
Current (A)
1. Place the ammeter,
in turn, at positions
1, 2, 3 and 4.
2. Record the
ammeter reading
at the points in the
table shown.
A3
A4
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For a parallel circuit, the current that leaves the cell or
battery is the same as the current that returns to the
cell or battery. The current does NOT get used up by a
circuit, just the energy the electrons are carrying.
A1 = A4
The current splits up at the first junction and then joins
together at the second junction. If the bulbs are
identical then the current will split evenly. If the bulbs
are NOT identical, then the current will NOT split
evenly. The following is always true for this circuit.
A1 = A2 + A3 =A4
© Boardworks Ltd 2003
REMEMBER:
In a series circuit the current is the same at any
point in the circuit.
A1 = A2 = A3
In a parallel circuit the current is being
split up at the first junction and then
joins together at the second junction..
A1 = A2 + A3 =A4
© Boardworks Ltd 2003
Summary for series circuits
1. In a series circuit the current is the same at
any point in the circuit.
2. The supply voltage is shared between the
components in a series circuit.
3. The current depends on the voltage in ANY
circuit.
© Boardworks Ltd 2003