Electrical Circuits - St Edmund's Girls'...
Transcript of Electrical Circuits - St Edmund's Girls'...
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Electrical Circuits
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source of energy
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?
a complete loop
a component no short circuits
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A model can help
us to understand
how current works
in an electric circuit.
What do the pizza shop and the
house of party-goers represent?
In this model, the
moped riders
represent the flow
of charge and the
pizzas represent
the electrical
energy carried
around the circuit.
How can we model electric circuits?
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What are conductors and insulators?
Conductors are materials
that allow the flow of
electric charge. Metals are
good conductors.
Insulators are materials that
do not allow the flow of
electric charge. Plastics are
good insulators.
In some materials, electric charges are free to flow, but in
others, they are not. This means the current cannot flow.
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The delocalized electrons are
free to flow through the metal
and so carry a current.
Insulating materials do not
contain free electrons and
so current is unable to flow.
Ionic solutions are also able
to conduct electricity
because they have mobile
charge-carrying particles.
It is the delocalized electrons involved in metallic bonding
that allow metals to conduct electricity.
delocalized electrons
How do metals conduct electricity?
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Does it conduct?
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Why do cables have plastic coatings?
To prevent electric shocks,
the metal wires are coated
with a thick layer of plastic.
Electricity and electric wires can be very dangerous.
Insulators can be used to make wires safer.
Metals, usually copper, are
used to make electrical wires
because they conduct current.
Plastic is an insulator and
does not conduct current.
How does this increase safety?
It is also important to insulate wires because if any part of
the circuit is earthed, the charge will not flow.
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Conductors and insulators
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Which competitor is finding it easier to build a circuit?
Using circuit diagrams
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Electronic circuits are
usually very complex.
It is important to have a
clear way of showing how
different components are
connected together.
A standard set of symbols
is used to represent
different devices and to
draw schematic diagrams
of circuits, which show
how the components
are connected.
Why use circuit diagrams?
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Wires or leads are used to carry
the current around a circuit
between the components.
circuit symbol for a wire
They are usually made from thin
copper wires twisted together and
covered with a plastic sleeve.
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 connectedtwo wires that cross
(i.e. not connected)
How are wires shown in circuit diagrams?
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What is the source of energy in a circuit?
When mains electricity is
unsuitable, cells or batteries
can be used as the source of
electrical energy.
Circuit symbol
for a cell
Mains electricity is often used
to power electric circuits.
This remote control uses batteries.
Circuit symbol
for a battery V
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Circuit components
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Circuit symbols
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Current will always pass along the path of least resistance.
The resistance of the wires in a circuit is low compared to
the resistance of components, such as bulbs.
The current can only
pass through the bulb.These circuits both
contain a short circuit, so
the bulb will not be lit up.
If current can flow along a path without passing through the
components this part of the circuit is called a short circuit.
What is a short circuit?
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Which circuit diagram?
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Current is a measure of the rate of flow of electric charge
in a circuit. Electric charge is measured in coulombs.
A
An ammeter must be
connected in series
as it measures the
current flowing
through it.
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.
What is current?
Current is measured in amperes
(A) using an ammeter. It is
calculated using the equation:
or I = Q
tcurrent = charge
time
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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.
The voltage of a battery is the “push”
it gives the charges in the circuit.
A 1 V cell gives 1 joule (J) of
energy to each coulomb of charge.
So, a 12 V battery gives 12 J of
energy to each coulomb of charge.
A voltmeter must be
connected in parallel
as it measures the
potential difference
across the component.
V
What is potential difference?
or V = W
Qvoltage =
work done
charge
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Water model of a circuit
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A cell is a source of electricity.
People often refer to cells as batteries, however they are not
the same and it is important to use the terms correctly!
A chemical reaction takes
place inside the cell,
which produces a
potential difference
(voltage) across the cell.
Are they cells or batteries?
A battery consists of two or more cells that are joined together.
The potential difference across a battery is the sum of the
potential differences across the cells.
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If several cells are connected in
series, the total voltage across
the battery can be found by
adding the voltages of the cells. 3V
4.5V
Using more cells in a battery
increases the voltage.
So, if 2 cells with a voltage
of 1.5V are connected
together, the voltage
across the battery is 3V.
When three cells of 1.5V are
connected, what is the
voltage across the battery?
V
1.5V
V
V
How can battery voltage be increased?
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Current and voltage – true or false?
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This way of representing the
direction of current is called
conventional current.
It is now know that charge is
carried by electrons, flowing
from the negative terminal
to the positive terminal.
This is called electron flow.
Before the discovery of the electron, scientists assumed that
current was due to positively-charged particles moving from
the positive terminal around a circuit to the negative terminal.
Today, both conventional current and electron flow can be
used to represent the direction of current.
What is conventional current?
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Representing current direction
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Glossary
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Anagrams
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Multiple-choice quiz