Conduction, convection and radiation
Temperature and heat
Temperature and heat are not the same thing because:
- temperature is a measure of how hot something is;
- heat is a measure of the thermal energy contained in an object;
- Temperature is measured in oC;
- Heat energy is measured in J.
Conduction
Metals are good A material which allows heat energy to move easily by conduction. Metals are good conductors because they contain free electrons. of heat energy. Non-metals and gases are usually poor conductors. Poor conductors are called insulators.
Heat energy is conducted from the hot end of an object to the cold end.
Conduction in solids
The All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. of a solid are held together by chemical bonds.
The atoms are fixed in place but are free to vibrate.
When part of a solid absorbs heat energy the atoms vibrate faster and with bigger amplitude.
These vibrations pass from atom to atom transferring heat energy as they do so.
This process happens in all solids when heated but is a slow process.
Conduction in metals
Some of the Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. in a 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 positively charged metal Electrically charged particle, formed when an atom or molecule gains or loses electrons..
When the free electrons absorb heat energy, they move much faster.
As they move through the metal, free electrons crash into metal ions.
Some of the Energy which an object possesses by being in motion. of the free electron is absorbed by the ions and it vibrates faster and with greater amplitude.
This process is very much faster than conduction caused by just passing vibrations from atom to atom.
Hence, conduction in metals is faster than in non-metals.
Image caption, Conduction in a solid
A solid is heated up
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Key points
- Conduction in insulators (non-metals) is only caused by passing vibrations from atom to atom.
- Conduction in good conductors (metals) is caused by collisions between fast moving free electrons and metal ions and by passing vibrations from atom to atom.
- Conduction by collisions between fast moving free electrons is very much faster than conduction by passing vibrations from atom to atom.
- Metals are good conductors because they contain free electrons.