Transcript Electrical Circuits

Electrical Circuits
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What is an electric circuit?
An electric circuit is
a path for electric
charge to flow along.
Like all electrical
devices, this
portable MP3 player
contains electric
circuits to enable it
to play music.
What is needed for an electric circuit to work?
 source of energy
 a complete loop
 a component
 no short circuits
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How are wires shown in circuit diagrams?
Wires or leads are used to carry
the current around a circuit
between the components.
They are usually made from thin
copper wires twisted together and
covered with a plastic sleeve.
circuit symbol for a wire
Circuit diagrams can be complex and it is important to be
able to distinguish between wires that are joined together
and those that cross without being joined.
two wires that
are connected
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two wires that cross
(i.e. not connected)
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What is the source of energy in a circuit?
Mains electricity is often used
to power electric circuits.
When mains electricity is
unsuitable, cells or batteries
can be used as the source of
electrical energy.
This remote control uses batteries.
Circuit symbol
for a cell
Circuit symbol
for a battery
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V
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Circuit components
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Which circuit diagram?
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What is current?
Current is a measure of the rate of flow of electric charge
in a circuit. Electric charge is measured in coulombs.
Current is measured in amperes
(A) using an ammeter. It is
calculated using the equation:
A
current = charge
time
or I = Q
t
A current of 1 A is 1 coulomb of
charge flowing every second.
So, a current of 5 A is 5 coulombs
of charge flowing every second.
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An ammeter must be
connected in series
as it measures the
current flowing
through it.
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What is potential difference?
Potential difference is the work done (or energy transferred)
between two points in a circuit, per coulomb of charge.
Potential difference is also called voltage.
Voltage is measured in volts (V) using a voltmeter.
voltage =
work done
or V = W
charge
Q
A 1 V cell gives 1 joule (J) of
energy to each coulomb of charge.
V
A voltmeter must be
connected in parallel
So, a 12 V battery gives 12 J of
as it measures the
energy to each coulomb of charge.
potential difference
The voltage of a battery is the “push” across the component.
it gives the charges in the circuit.
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How can battery voltage be increased?
Using more cells in a battery
increases the voltage.
If several cells are connected in
series, the total voltage across
the battery can be found by
adding the voltages of the cells.
So, if 2 cells with a voltage
of 1.5 V are connected
together, the voltage
across the battery is 3 V.
When three cells of 1.5 V are
connected, what is the
voltage across the battery?
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1.5 V
V
3V
V
4.5 V
V
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Current and voltage – true or false?
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