# 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)
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.
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.
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.
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:
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.
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.