Energy Resources and Energy Transfer

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Energy Resourcesand Energy Transfer
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Contents

• Thermal Energy Transfer
• Efficiency
• Energy Resources
• Work, Power and Energy
• Electromagnetic Forces
• Electromagnetic Induction

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Heat Transfer
Heat is transferred in order to equalise the
temperatures of the object and its environment
A cup of coffee will cool down because it is
giving out heat energy into the surroundings
This drink (taken out of the fridge) will warm up
because it is taking in heat energy from the
surroundings
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Conduction

• Atoms in a substance are always vibrating. If the
  substance gets hotter, the atoms vibrate more.
  The heat energy is given to the atoms, which
  makes them move about faster
• Every time they collide with another atom, the
  heat energy is transferred
• This is how heat travels through a solid

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Convection

• Hot air rises in cold air. Hot water rises in
  cold water
• This is called convection
• When hot air rises, colder air has to move in to
  replace it
• Convection cannot happen in solids, as the atoms
  aren't able to move around

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Radiation

• Hot objects radiate heat to their colder
  surroundings
• Black and dull surfaces emit and absorb radiation
  well
• White and shiny surfaces do not emit radiation
  well and reflect radiation instead of absorbing it

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Insulation

• Air can convect the heat energy away from a house
  if it is able to move. If the air is trapped in
  small spaces it can't move so it doesn't convect
  the heat energy
• Fibreglass keeps the air still
• Trapped air insulates heat by not allowing it to
  escape
• Double glazing works in this way

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Power

• Which boils quicker?
• Kettle with high power rating
• or Kettle with low power rating
• Power how quickly the energy is transferred
• (from electrical to heat energy)
• High power Kettle heats up quickly
• Low power Kettle heats up slowly

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Power
The power rating of a light bulb...
Power how much energy is given to an
appliance per unit of time
Power (Watts) voltage x current
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Cost of Electricity
? Number of units power rating x time used
1 unit 1kWh
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Efficiency

• Power energy transfer per second
• Power energy transferred/time taken
• (W) (J) (sec)
• During a movement or change of state (etc.)
  energy is usually lost as heat energy to the
  surroundings
• The energy inputted is therefore always higher
  than the useful energy taken out
• Efficiency (useful energy out/energy in) x 100
  

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Non-Renewable Fuels

• All power stations generate electricity
• - Fuel is used to produce heat energy
• - The heat energy heats water and turns it into
  steam
• - The steam is pushed at high pressure along
  pipes to the turbines
• - The steam makes the turbines spin, turning a
  generator which then produces electricity
• - The electricity is then supplied to houses,
  factories and schools via the national grid
• Non-renewable (fossil) fuels are oil, gas and
  coal

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Nuclear Fuels

• Uranium is the fuel used in many nuclear power
  stations
• Uranium is not burnt like coal or gas but
  undergoes nuclear fission
• Atoms of uranium are split up which releases
  large amounts of energy
• Nuclear fission produces harmful radiation so
  people are sceptical
• Waste from these reactions is also radioactive
• Accidents are serious but very rare

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Electromagnetic Forces

• A current (I) has a magnetic field (B) around it
• A wire has a circular magnetic field around it
• If the current changes direction, so does the
  field

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Electromagnetic Forces

• Magnets attract magnetic materials using a
  magnetic field
• The magnetic field surrounds the magnet, and gets
  weaker as the distance from the magnet increases
• Magnets should be called permanent magnets
• ? the magnetism is always there
• Electricity makes a magnet much stronger
• This can be turned on and off

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Electromagnetic Forces

• Magnets pick up paper clips etc.
• Electromagnets pick up cars etc.

strong
weak
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Electromagnetic Forces

• The magnetic field around a coil electromagnet
  can be increased by
• - Increasing the current flowing through the
  wire
• - Adding loops on the coil (loops are long
  lengths of wire)
• - Placing an iron or steel core inside the coil
• Basic electromagnet

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Electromagnetic Forces

• The Motor Effect
• - When two magnets are placed close to each
  other, they the fields affect each other produce
  a force
• If a wire carrying a current is placed inside
  this magnetic field, a force is produced. This is
  called the motor effect
• The direction of the force will depend on the
  direction of the magnetic field and the direction
  of the current in the field

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Electromagnetic Forces

• Flemings Left Hand Rule
• - When creating a force, use Flemings LH Rule
  to determine in which way the motor will spin
• -

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Electromagnetic Forces

• We can increase the force produced by
• - increasing the current
• - increasing the number of coils
• - increasing the magnetic field strength
  (stronger magnet)

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Electromagnetic Induction

• When a magnet is moved into a coil, an
  electrical current is induced

• When the magnet stops,
• the induced current stops

• When the magnet reverses, the electrical current
  reverses

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Electromagnetic Induction

• Increase the voltage? 3 ways
• Stronger magnet
• 2. Speed of magnet
• 3. Number of coils

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Transformers
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Transformers
4 coils produce 10V
8 coils produce 20V
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Transformers
Power stations step-up the voltage to reduce
energy losses (but v high voltage) Pylons to
houses step-down the voltage to reduce risk of
electrocution
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Summary

• Thermal energy is transferred by conduction,
  convection and radiation
• Efficiency (useful output/total input) x 100
• Fossil fuels are widely used energy resources but
  these are non-renewable
• E PxT, P V x I, units power (kW) x time
  (hr)
• Electromagnetic forces are used to create
  movement
• Movement is used to create voltage using
  electromagnetic induction