4 Energy resources and energy transfers - iGCSE Physics Edexcel

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4.1 use the following units: kilogram (kg), joule (J), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s) and watt (W)
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Terms in this set (19)
4.1 use the following units: kilogram (kg), joule (J), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s) and watt (W)
Mass = kilogram (kg)
energy = joule (J)
velocity = metre/second (m/s)
acelleration = metre/ second 2 (m/s2)
force = newton (N)
time = second (s)
power = watt (W)
4.2 describe energy transfers involving energy stores: • energy stores: chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, nuclear • energy transfers: mechanically, electrically, by heating, by radiation (light and sound)
KINETIC-energy of moving object
GRAVITATIONAL-energy gained when object is lifted up, and lost when falling
ELASTIC-energy of a stretched spring or elastic band
ELECTROSTATIC-energy due to forces of attraction or repulsion between two charges
MAGNETIC-energy due to forces of attraction or repulsion between two magnets
CHEMICAL-energy contained in a chemical substance
THERMAL-energy something has due to it's temperature
NUCLEAR-energy contained within the nucleus of an atom


TRANSFERS
MECHANICALLY-when a force acts of a body, energy can be transferred between stores
ELECTRICALLY-electricity can transfer energy from a power source, delivering it to components in a circuit
HEATING-thermal energy can be transferred from place to place by the processes of Conduction Convection and Radiation
RADIATION-light and sound carry energy and can transfer it between places.
4.3 use the principle of conservation of energy
-In any process energy is never created or destroyed.
-Can only be moved from one store to another.
4.4 know and use the relationship between efficiency, useful energy output and total energy output: Efficiency = useful energy output / total energy input x 100%
Efficiency
=
useful energy output
-----------------------------
total energy input
x
100%
Image: 4.4 know and use the relationship between efficiency, useful energy output and total energy output: Efficiency = useful energy output / total energy input x 100%
4.5 describe a variety of everyday and scientific devices and situations, explaining the transfer of the input energy in terms of the above relationship, including their representation by Sankey diagrams
The efficiency of a system can be represented using a Sankey diagram
The arrow in a Sankey diagram represents the transfer of energy:
The end of the arrow pointing to the right represents the energy that ends up in the desired store - the useful energy output.
The end that points down represents the wasted energy.
The width of each arrow is proportional to the amount of energy going to each store.
4.6 describe how thermal energy transfer may take place by conduction, convection and radiation
CONDUCTION
Main method of thermal energy transfer in solids.
When a material is heated, the atoms start to move around vibrate more.
As they do so they bump into each other, transferring energy from atom to atom.
4.7 explain the role of convection in everyday phenomena
CONVECTION
Main way that heat travels through liquids and gases.

The molecules push each other apart, making the liquid/gas expand.
This makes the hot liquid/gas less dense than the surroundings.
The hot liquid/gas rises, and the cooler (surrounding) liquid/gas sinks down to take its place.
Eventually the hot liquid/gas cools, contracts and sinks back down again.
Image: 4.7 explain the role of convection in everyday phenomena
4.8 explain how emission and absorption of radiation are related to surface and temperature
RADIATION
All hot objects give off thermal radiation: The hotter they are, the more they emit.
Thermal radiation is part of the electromagnetic spectrum - Infrared.
Thermal radiation is the only way in which heat can travel through a vacuum.
The colour of an object affects how good it is at emitting and absorbing thermal radiation:
4.9 practical: investigate thermal energy transfer by conduction, convection and radiation
Insulated beakers (INSULATION EFFECT):
The three beakers shown above will lose heat at different rates.
The one in the middle is surrounded by insulation, reducing heat loss by conduction.
The one on the right has a lid, reducing heat loss by convection.
The one on the left has no insulation - it is a control, allowing a fair comparison to be made.

Coloured beakers (COLOUR EFFECT):
The two beakers above are the same, but one has been painted black, whilst the other has been painted silver.
Black is a better emitter of thermal radiation than silver and so we would expect the black beaker to cool faster than the silver beaker.
In the above two experiments there are a number of things that must be done in order to make the experiment fair tests:
The beakers must be identical (apart from the change in colour or insulation).This means they must be the same shape, the same size and the same material.
If filled with water (or some other substance) they must contain equal amounts.
They must also start at the same temperature.
4.10 explain ways of reducing unwanted energy transfer, such as insulation
Poor conductors of heat are called Insulators

Most insulators contain pockets of trapped air.

Air is a very poor conductor of heat (as are all gases).

Trapping the air prevents it from moving around, forming a convection current.

Include covering the material with a shiny (non-metal) coating - to reduce the emission or absorption of thermal radiation.

Putting a lid on a beaker to prevent air carrying heat away by convection.
4.11 know and use the relationship between work done, force and distance moved in the direction of the force: work done = force × distance moved W = F × dWork Done (J) = Force (N) x distance moved (m) W=F*d4.12 know that work done is equal to energy transferredEnergy is the capacity of some thing to do work. Whenever any work is done, energy gets transferred (mechanically) from one store to another. The amount of energy transferred (in joules) is equal to the work done (also in joules).4.13 know and use the relationship between gravitational potential energy, mass, gravitational field strength and height: gravitational potential energy = mass × gravitational field strength × height GPE = m × g × hGravitational potential energy (J) = Mass (kg) x gravitational field strength (N/kg) x height (m) GPE = m × g × h g=10kg4.14 know and use the relationship: kinetic energy = 1/2 × mass × speed^2Kinetic energy (J) = 0.5 x mass (kg) x velocity (m/s)^24.15 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and workEnergy cannot be created or destroyed, it can only be transferred from one type (store) to another. A falling object (in the absence of air resistance): GPE is transferred into KE. The KE just before the object reaches the ground will equal the GPE that it loses. An engine causing a car to speed up: The work done by the engine will cause a transfer of chemical energy (of the fuel) into kinetic energy. A car applying its brakes: The brakes do work, which causes some of the car's KE to be transferred into Thermal (Heat) energy (the brakes get hotter).4.16 describe power as the rate of transfer of energy or the rate of doing workpower is the transfer of energy per second, or the rate4.17 use the relationship between power, work done (energy transferred) and time taken: time takenpower = work done / time taken P = W / t Unit of power is W, same as J/s4.18P describe the energy transfers involved in generating electricity using: • wind • water • geothermal resources • solar heating systems • solar cells • fossil fuels • nuclear power4.19P describe the advantages and disadvantages of methods of large-scale electricity production from various renewable and non-renewable resources