Heat and Temperature
- Heat is the amount of thermal energy something has.
- It is measured in Joules or Kilojoules (J or KJ).
- Temperature is a measure of how hot or cold something is.
- It is measured in degrees C.
- Specific heat is the amount of joules needed to raise 1g of a substance 1 degrees C.
- Heat transfer is always from hot to cold.
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- Conduction can take place in a solid, liquid or gas.
- It is the main method of heat transfer in solids.
- Gas and liquids are not good conductors of heat as their particles are spread out.
- In conduction heat energy is turned in to kinetic energy.
- This makes particles vibrate which hit their neighbours and this happens all the way from the heat source to the cold end of the substance.
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- Metals contain free electrons which do not belong to a specific atom.
- The atom without the electron is a charged metal ion. The electrons hit into the ions which makes them vibrate even more.
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- Convection can only take place in a liquid or a gas as the particles in a solid only vibrate they do not move.
- Heaters use convection to heat rooms.
- The heater heats the air around it which rises as it becomes less dense than the air above it.
- As this air moves up cold air takes its place.
- This air is then heated so it rises then cools, becomes denser that the air below it and sinks where it is heated again.
- This is called a convection current and it takes place in the sun.
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- Radiation is the only method of heat transfre that does not require a substance to travel through.
- Radiation is transfered by electromagnetic waves.
- The waves are infrared waves.
- Infrared waves have a wavelength between 0.72 and 10 micrometers.
- Shiny silvery surfaces reflect radiation the best while dark surfaces absorb the best.
- All things emmit radiation but the larger the mass the more radiation absorbed and emmited.
- This type of radiation is called thermal radiation.
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