Module 5: Energy and Electricity

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Module 5Energy and Electricity
Mr Hawkridge
Marlborough School Science Faculty
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Energy Electricity

• Current
• Voltage
• Resistance
• Variable Resistance
• The Heating Effect
• Electrical Costs

• Protecting the User
• Fuses
• National Grid
• Generating Electricity
• Saving Electricity
• Insulators

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Measuring Current
21 February, 2005
Marlborough School Science Faculty
AIMS

• To revise series/parallel circuits to examine
  how current behaves in a circuit

Mr Hawkridge
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Basic Electricity

• You Should Know
• Current is the flow of electrons
• A voltage (potential difference) is required to
  make the electrons move in a particular direction
• Current is measured in amperes (amps, A) using an
  ammeter
• An electrical circuit needs 3 things a power
  supply, wires, an electrical component
• The two main types of circuit are series and
  parallel

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Basic Electricity

• Current
• A flow of electrons
• A voltage (potential difference) is required to
  make the electrons move in a particular direction
• Current is measured in Amps using an ammeter
• A complete circuit is required for current to
  flow
• Two main types of circuit series and parallel

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Basic Electricity

• AC and DC
• If the pd makes the current flow in one direction
  only this is a Direct Current
• If the pd makes the current constantly change
  direction then this is an Alternating Current

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Basic Electricity

• Resistance
• This is the opposition to current flow
• Resistance is measured in Ohms
• As the resistance increase the current decreases
• Graphs of current against voltage also show how
  the resistance changes
• Be aware of the current voltage graphs for
• Lamps, diodes, thermistors, resistors

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7J Connecting circuits Making electrical
objects work
What are they?
What must happen for the electrical device to
work?
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Measuring Current
21 February, 2005
Marlborough School Science Faculty
AIMS

• To revise series/parallel circuits to examine
  how current behaves in a circuit

Mr Hawkridge
10
More Circuit Diagrams

• Look at the question below from Fridays
  Homework. Which circuit is the odd one out?
  Explain.

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7J Circuits and current Current in a series
circuit
Is the current used up?
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7J Circuits and current Current in a parallel
circuit
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Measuring Voltage
22 February, 2005
Marlborough School Science Faculty
AIMS

• To learn how to connect a voltmeter to measure
  voltage across electrical components

Mr Hawkridge
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Measuring Voltage

• You Should Know
• Voltage is also known as potential difference
• This is the push on the electrons
• It is the energy supplied to each packet (or
  Coulomb) of electrons
• Measured in Volts (V) using a voltmeter
• As the voltage increases so does the current

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Measuring Voltage

• A voltmeter must be attached in parallel to
  measure the potential difference across a
  component (unlike an ammeter which must be used
  in series)

X
V
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Resistance
24 February, 2005
Marlborough School Science Faculty
AIMS

• Explain how a resistor affects electric current
• Use the formula V IR

Mr Hawkridge
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Resistance

• Batteries provide direct current, because the
  current flows only one way around the circuit.
• The units of current are amps (A).
• An ammeter must be placed in series in a circuit
  to measure current.
• A voltmeter must be placed in parallel in a
  circuit to measure potential difference (pd).

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• SERIES
• The amount of current is the same at all points
  in a series circuit
• The voltage however divides among series
  components. The voltage across individual
  components will add up to the total voltage
• PARALLEL
• The amount of current is divided according to
  resistance.
• Voltage is the same for all parallel components
  and is equal to the total voltage

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Current-Voltage Graphs
3 March, 2005
Marlborough School Science Faculty
AIMS

• To describe how current varies with voltage for
  resistors and diodes

Mr Hawkridge
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Current-Voltage Graphs

• We know that current (I) is proportional to
  voltage (V) (this is where VIR comes from)
• If we plot voltage versus current we get
  different shape graphs for different components
• You will need to know about 4 graphs
• Ohmic conductor
• Filament lamp
• Thermistor
• Diode

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• The steeper the graph, the lower the resistance
• The flatter the graph, the higher the resistance

I
V
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Current-Voltage Graphs

• Match the component to the graph and the
  explanation

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Current-Voltage Graphs

• Set up the circuit below, substituting different
  components for X
• Make at least 6 pairs of readings at various
  voltages
• Make a graph of current versus voltage for each
  component

A
V
X
variable
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Variable Resistors
10 March, 2005
Marlborough School Science Faculty
AIMS

• To describe how the resistance of a LDR can
  change with light intensity

Mr Hawkridge
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The Heating Effect
10 March, 2005
Marlborough School Science Faculty
AIMS

• To explain why a resistor heats up in terms of
  energy released by collisions

Mr Hawkridge
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The Heating Effect

• STARTER
• A piece of nichrome wire is kept at a steady
  temperature. Different voltages are applied and
  the current measured. Fill in the missing values
  for the resistance.

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The Heating Effect

• What would happen if you used a longer wire?
• What would happen if you used a shorter wire?
• What else could change about the wire that would
  affect the current at which it burned out?
• Give 2 practical uses of the heating effect of a
  wire

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Electrical Costs
8 March, 2005
Marlborough School Science Faculty
AIMS

• To calculate electricity consumption measured in
  kilowatt hours (kWh)

Mr Hawkridge
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Electrical Costs

• You Should Know
• The more current a devices uses the more energy
  is transferred
• The higher the voltage supplied the more energy
  is available
• Cost Power x Time x Unit cost
• () (kW) x (h) x (/kWh)

Q A toaster has a power rating of 2 kW. It is
switched on and the toast is done after 3
minutes. If the power company charge 9p for each
kWh how much does it cost to use the toaster?
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Electrical Costs

• You Should Know
• The more current a devices uses the more energy
  is transferred
• The higher the voltage supplied the more energy
  is available
• Cost Power x Time x Unit cost
• () (kW) x (h) x (/kWh)

A Power 2 kW Time 3/60min 0.05 h Unit
cost 9p 0.09 So, Cost (2 kW) x (0.05 h) x
(0.09) 0.009
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Electrical Costs
Calculate the missing values based on a cost of
8p per kilowatt hour
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Electrical Costs
Calculate the missing values based on a cost of
8p per kilowatt hour
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The National Grid
14 March, 2005
Marlborough School Science Faculty
AIMS

• Recall that the mains delivers alternating
  current (AC)
• To learn how electricity is generated and the
  impact on the environment

Mr Hawkridge
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The National Grid

• Electricity is made by moving a coil of wire near
  a magnet
• The aim of any power station is to move the coil
  of wire near a magnet
• Fossil fuels can be burnt to produce steam which
  can turn turbines which turn generators to make
  electricity
• The disadvantage is that they are non-renewable
  and also polluting

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The National Grid

• This is the system of wires carrying the
  electricity around the country
• The wires get hot as current moves through them
  and so a lot of energy can be wasted
• The wasted energy can be reduced by sending the
  electricity through the wires at a lower current
  and a high voltage
• A transformer can be used to increase or decrease
  voltages

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Transformers
Transformers are used to _____ __ or step down
_______. They only work on AC because an
________ current in the primary coil causes a
constantly alternating _______ ______. This will
_____ an alternating current in the secondary
coil.
Words alternating, magnetic field, induce, step
up, voltage
We can work out how much a transformer will step
up or step down a voltage
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Some transformer questions
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Some example questions

• A transformer increases voltage from 10V to 30V.
  What is the ratio of the number of turns on the
  primary coil to the number of turns on the
  secondary coil?
• A step-down transformer has twice as many turns
  on the primary coil than on the secondary coil.
  What will be the output (secondary) voltage if
  the input voltage is 50V?

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Electrical Safety
16 March, 2005
Marlborough School Science Faculty
AIMS

• To explain why mains electricity is dangerous.
  Give some ways the user is protected

Mr Hawkridge
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The National Grid
Electricity reaches our homes from power stations
through the National Grid
If electricity companies transmitted electricity
at 240 volts through overhead power lines there
would be too much ______ loss by the time
electricity reaches our homes. This is because
the current is ___. To overcome this they use
devices called transformers to step up the
voltage onto the power lines. They then ____
____ the voltage at the end of the power lines
before it reaches our homes. This way the
voltage is _____ and the current and power loss
are both ____.
Words step down, high, power, low, high
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Electrical Safety 2
17 March, 2005
Marlborough School Science Faculty
AIMS

• To learn how to select the correct fuse for an
  appliance
• To know how a plug is wired safely

Mr Hawkridge
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Wiring a plug
Earth wire
Live wire
Fuse
Neutral wire
Cable grip
Insulation
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Power and fuses
Power is the rate of doing work. The amount of
power being used in an electrical circuit is
given by
Power voltage x current in W in V
in A
Using this equation we can work out the fuse
rating for any appliance. For example, a 3kW
(3000W) fire plugged into a 240V supply would
need a current of _______ A, so a _______ amp
fuse would be used (fuse values are usually 3, 5
or 13A).
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Power and fuses
Copy and complete the following table
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Transformers
21 March, 2005
Marlborough School Science Faculty
AIMS

• To use a formula to calculate voltage changes
  across a transformer

Mr Hawkridge
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Fuses
Fuses are _______ devices. If there is a fault
in an appliance which causes the ____ and neutral
(or earth) wire to cross then a ______ current
will flow through the _____ and cause it to
_____. This will break the _______ and protect
the appliance and user from further _____.
Words large, harm, safety, melt, live, circuit,
fuse
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Circuit Breakers
21 March, 2005
Marlborough School Science Faculty
AIMS

• To learn what a residual current circuit breaker
  (RCCB) is

Mr Hawkridge
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Circuit Breakers

• A residual current circuit breaker (or RCCB)
  detects any difference between the currents in
  the live and neutral wires
• It quickly breaks the circuit preventing the user
  from being electrocuted
• It can be easily reset if tripped accidentally

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Circuit Breakers

• Some appliances do not have an earth wire
• They are safe because the casing is made from an
  insulator like plastic so current cannot flow
  through it
• This is the symbol for a double insulated device

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Earth wires
Earth wires are always used if an appliance has a
_____ case. If there is a _____ in the
appliance, causing the live wire to ______ the
case, the current _______ down the earth wire
and the ______ blows.
Words fuse, fault, metal, surges, touch
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Insulators
12 April, 2005
Marlborough School Science Faculty
AIMS

• To understand that insulation can reduce unwanted
  energy transfer

Mr Hawkridge
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• STARTER
• Match each thing to its most likely source of
  electricity
• Large steel works Solar cells
• Calculator Rechargeable battery
• Farm in Scotland On-site power station
• Smoke alarm Wind turbines
• Family home The National Grid
• Mobile home Long-life ordinary battery

• Select one of the electricity sources and give
  some advantages and disadvantages of its use

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Insulators

• Heat flows through the walls, windows, and
  ceiling transferring heat energy outside

3 Main ways to Insulate -loft insulation -double
glazing -cavity wall insulation
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House insulation
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Insulators

• Why does this house loose less energy than a
  conventional house?

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Insulators
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Integer House - Watford
A heat pump pushes cold water down 50m into the
Earth where it is heated by the ground and
returns to the surface at a warm temperature.  
Solar water heaters mounted on the roof can
provide free hot water at up to 95c   A waste
system treats and recycles water used for washing
and bathing reducing water usage by 30  
Rainwater is collected, treated and stored in
an underground tank for garden irrigation and car
washing
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An Efficient House

• Activity
• Your task is to design an energy efficient house
  using a full sheet of paper
• What kinds of technology will your house use?
• How will its shape or layout help save energy?
• Will it use any renewable energy resources? (ex.
  Solar or wind power)
• Where energy is wasted and how this loss can be
  avoided or reduced
• You MUST label and briefly explain the features
  of your house

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Saving Energy
13 April, 2005
Marlborough School Science Faculty
AIMS

• To assess the economic and environmental cost of
  wasted energy

Mr Hawkridge
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House insulation
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Saving Energy