Electric circuits
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Transcript of Electric circuits
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D.OWINO 2014
ELECTRICAL ELECTRICAL CIRCUITSCIRCUITS
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The CELLThe CELL
The cell stores chemical energy and transfers
it to electrical energy when a circuit is
connected. When two or more cells are
connected together we call
this a Battery.
The cells chemical energy is
used up pushing a current
round a circuit.
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What is an electric current?
An electric current is a flow of microscopic
particles called electrons flowing through
wires and components.
+ -
In which direction does the current flow? from the Negative terminal to the Positive terminal of a cell.
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simple circuitssimple circuits
Here is a simple electric circuit. It has a cell, a
lamp and a switch.
To make the circuit, these components are
connected together with metal connecting wires.
cell
lamp
switch
wires
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simple circuitssimple circuitsWhen the switch is closed, the lamp lights up. This is because there is a continuous path of metal for the electric current to flow around.
If there were any breaks in the circuit, the current could not flow.
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circuit diagramcircuit diagram
cell switch
lamp
wires
Scientists usually draw electric circuits using symbols;
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circuit diagramscircuit diagramsIn circuit diagrams components are represented by the following symbols;
cell battery
switch
lamp
motorammeter
voltmeter
buzzer
resistor
variable resistor
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types of circuittypes of circuit
There are two types of electrical circuits;
SERIES CIRCUITS PARALLEL CIRCUITS
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The components are connected end-to-end, one after the other.
They make a simple loop for the current to flow round.
SERIES CIRCUITS
If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.
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PARALLEL CIRCUITS
The current has a choice of routes.
The components are connected side by side.
If one bulb ‘blows’ there is still be a complete circuit to the other bulb so it stays alight.
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measuring current
Electric current is measured in amps (A)
using an ammeter connected in series in
the circuit.
A
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measuring current
A A
This is how we draw an ammeter in a circuit.
SERIES CIRCUIT PARALLEL CIRCUIT
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measuring currentSERIES CIRCUIT
PARALLEL CIRCUIT
• current is the same
at all points in the
circuit.
2A 2A
2A
• current is shared between the components
2A2A
1A
1A
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copy the following circuits and fill in the missing ammeter readings.
?
?
4A
4A
4A
3A?
?
1A
?
3A
1A
1A
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measuring voltage
The ‘electrical push’ which the cell gives to the
current is called the voltage. It is measured in
volts (V) on a voltmeter
V
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Different cells produce different voltages. The
bigger the voltage supplied by the cell, the bigger
the current.
measuring voltage
Unlike an ammeter a voltmeter is connected
across the components
Scientist usually use the term Potential
Difference (pd) when they talk about voltage.
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measuring voltage
V
This is how we draw a voltmeter in a circuit.
SERIES CIRCUIT PARALLEL CIRCUIT
V
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V
measuring voltage
VV
V
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series circuit
1.5V
• voltage is shared between the components
1.5V
3V
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• voltage is the same in all parts of the circuit.
3V
parallel circuit
3V
3V
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measuring current & voltage
copy the following circuits on the next two slides.
complete the missing current and voltage readings.
remember the rules for current and voltage in series and parallel circuits.
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measuring current & voltage
V V
6V4A
A
A
a)a)
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measuring current & voltage
V
V
6V4A A
A
A
b)b)
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answers
3V 3V
6V
4A 4A6V
6V
6V4A 4A
2A
2A
4A
a)a) b)b)