AQA P1a Heat Transfer

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Heat transfer and efficiency
Heat can be transferred from place to place by conduction, convection and radiation.
Dark matt surfaces are better at absorbing heat energy than light shiny surfaces.
Heat energy can be lost from homes in many different ways and there are ways of
reducing these heat losses.
There are several different types of energy, and these can be transferred from one
type to another. Energy transfer diagrams show the energy transfers in a process.
More efficient devices transfer the energy supplied to them into a greater
proportion of useful energy than less efficient devices do.
Heat transfer by conduction and convection
Heat is thermal energy. It can be transferred from one place to another by conduction,
convection and radiation. Conduction and convection involve particles, but radiation
involves electromagnetic waves.
Conduction
Thermogram of a pan being heated on a stove
Heat energy can move through a substance by conduction. Metals are good conductors
of heat, but non-metals and gases are usually poor conductors of heat. Poor conductors
of heat are called insulators. Heat energy is conducted from the hot end of an object to
the cold end.
The electrons in piece of metal can leave their atoms and move about in the metal as free
electrons. The parts of the metal atoms left behind are now charged metal ions. The ions
are packed closely together and they vibrate continually. The hotter the metal, the more
kinetic energy these vibrations have. This kinetic energy is transferred from hot parts of
the metal to cooler parts by the free electrons. These move through the structure of the
metal, colliding with ions as they go.
Heat transfer by conduction

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Convection
Liquids and gases are fluids. The particles in these fluids can move from place to place.
Convection occurs when particles with a lot of heat energy in a liquid or gas move and
take the place of particles with less heat energy. Heat energy is transferred from hot
places to cooler places by convection.
Liquids and gases expand when they are heated. This is because the particles in
liquids and gases move faster when they are heated than they do when they are cold.…read more

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Heat transfer by radiation
Radiation
All objects give out and take in thermal radiation, which is also called infrared
radiation. The hotter an object is, the more infrared radiation it emits.
Light from the sun reaching earth
Infrared radiation is a type of electromagnetic radiation that involves waves. No particles
are involved, unlike in the processes of conduction and convection, so radiation can even
work through the vacuum of space.…read more

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Heat escape routes
Take a look at this image showing heat loss from a house.
red shows where most heat is lost - through the windows and roof
Heat is lost:
through the roof
through windows
through gaps around the door
through the walls
through the floor
Heat energy is transferred from homes by conduction through the walls, floor, roof and
windows. It is also transferred from homes by convection.…read more

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Forms of energy
You should be able to recognise the main types of energy. One way to remember the
different types of energy is to learn this sentence:
Most Kids Hate Learning GCSE Energy Names
Each capital letter is the first letter in the name of a type of energy.
Types of energy
Type of energy Description
Magnetic Energy in magnets and electromagnets
Magnet
Kinetic The energy in moving objects. Also called movement energy.…read more

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Organic food
Sound Energy released by vibrating objects
Guitar
Electrical Energy in moving or static electric charges
Lightning
Elastic potential Stored energy in stretched or squashed objects
Catapult
Nuclear Stored in the nuclei of atoms
Nuclear fuel assembly
Energy transfer
Different types of energy can be transferred from one type to another. Energy transfer
diagrams show each type of energy, whether it is stored or not, and the processes taking
place as it is transferred.…read more

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Process of using chemical energy
This diagram shows the energy transfer diagram for the useful energy transfer in an
electric lamp. You can see that the electric lamp transfers or converts electrical
energy into light energy.
Process of using electrical energy
Notice that these energy transfer diagrams only show the useful energy transfers.
However, car engines are also noisy and hot, and electric lamps also give out heat
energy.
Sankey diagrams
Sankey diagrams summarise all the energy transfers taking place in a process.…read more

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Energy cannot be created or destroyed. It can only be transferred from one form to
another or moved. Energy that is 'wasted', like the heat energy from an electric lamp,
does not disappear. Instead, it is transferred into the surroundings and spreads out so
much that it becomes very difficult to do anything useful with it.
Electric lamps
Ordinary electric lamps contain a thin metal filament that glows when electricity passes
through it.…read more

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Note that the efficiency of a device will always be less than 100%.…read more

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