Temperature & Heat: Heat Transfer

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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 Irradiance

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

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