Temperature & Heat: Heat Transfer

Conduction Transfer of heat within a substance, molecule by molecule Occurs through rapid vibration of atoms and molecules These vibrating molecules interact with neighbouring particles, transferring some of their energy (heat) to them This vibration travels from the hotter end to the cooler end of the object

Substances in which conduction occurs easily are called thermal conductors (e.g. metals) Substances in which it only occurs a little are called thermal insulators

U- value The amount of heat energy conducted per second through 1 metre squared of a structure when a temperature difference of 1 K is maintained between its ends A good insulator has a low U-value

Convection The transfer of heat from one place to another by the movement of fluids When the fluid is heated, it expands and becomes less dense It rises through the cooler fluid above it This movement of fluid is called a convection current Main method of heat transfer in liquids and gases

Radiation Transfer of heat by means of electromagnetic waves The higher the temperature, the shorter the wavelengths of emitted waves Darker surfaces are better at radiating and absorbing heat than bright or shiny ones Heat from the sun is radiated heat

Solar IrradianceAverage amount of the Sun's energy falling per second perpendicularly on 1 metre squared of the Earth's atmosphere

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