Transcript Energy Resources and Energy Transfer

Energy Resources
and Energy Transfer
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
Conduction
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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
Convection
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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
Radiation
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Hot objects radiate heat to their
colder surroundings
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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
Insulation
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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
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
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
P
V
I
Cost of Electricity
1 unit = 1kWh  Number of units = power rating x time used
Efficiency

Power = energy transfer per second
E
P
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T
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 = %
Non-Renewable Fuels
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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
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Non-renewable (fossil) fuels are oil, gas and coal
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
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A current (I) has a magnetic field (B) around it
A wire has a circular magnetic field around it
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If the current changes direction, so does the field
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Electromagnetic Forces
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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
Electromagnetic Forces
Magnets pick up paper clips etc.
strong
weak
Electromagnets pick up cars etc.
Electromagnetic Forces
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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
Electromagnetic Forces
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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
Electromagnetic Forces
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Fleming’s Left Hand Rule:
- When creating a force, use Fleming’s LH Rule to determine in
which way the motor will spin
-
Electromagnetic Forces
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We can increase the force produced by:
- increasing the current
- increasing the number of coils
- increasing the magnetic field strength (stronger magnet)
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
Electromagnetic Induction
Increase the voltage? … 3 ways…
1. Stronger magnet
2. Speed of magnet
3. Number of coils
Transformers
Transformers
4 coils produce 10V 8 coils produce 20V
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
Summary
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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