Energy will always flow from areas at high temperatures to areas at low temperatures. This is called thermal transfer. Thermal energy can be transferred in three main ways: conduction, convection and radiation. CONDUCTION:
Materials that allow thermal energy to transfer through them quickly are called thermal conductors. Those that do not are called thermal insulators. If one end of a conductor is heated, the atoms that make up its structure start to vibrate more vigorously. As the atoms in a solid are linked together by chemical bonds, the increased vibration can be passed on to other atoms. The energy of movement passes through the whole material. Conduction cannot occur when there are no particles present, so a vacuum is a perfect insulator. CONVECTION:
Convection occurs in liquids and gases because these materials flow. The particles in a fluid move all the time. When a fluid is heated, energy is transferred to the particles, causing them to move faster and further apart. This makes the heated fluid less dense than the unheated fluid. The less dense warm fluid will rise above the more dense colder fluid, causing the fluid to circulate. This convection current is how the thermal energy is transferred.
If a fluid's movement is restricted, then energy cannot be transferred. That is why many insulators, such as ceiling tiles, contain trapped air pockets. Wall cavities in houses are filled with fibre to prevent air from circulating and transferring thermal energy by convection. RADIATION:
Radiation, unlike convection and conduction, does not need particles at all. Radiation can travel through a vacuum. This is clearly shown by the radiation that arrives from the sun. Radiated heat energy is carried mainly by infra-red radiation, which is part of the electromagnetic spectrum.
All objects take in and give out infra-red radiation all the time. Hot objects radiate more infra-red than cold objects. The amount of radiation given out or absorbed by and object depends on its temperature and on its surface.
Materials that allow thermal energy to transfer through them quickly are called thermal conductors. Those that do not are called thermal insulators. If one end of a conductor is heated, the atoms that make up its structure start to vibrate more vigorously. As the atoms in a solid are linked together by chemical bonds, the increased vibration can be passed on to other atoms. The energy of movement passes through the whole material. Conduction cannot occur when there are no particles present, so a vacuum is a perfect insulator. CONVECTION:
Convection occurs in liquids and gases because these materials flow. The particles in a fluid move all the time. When a fluid is heated, energy is transferred to the particles, causing them to move faster and further apart. This makes the heated fluid less dense than the unheated fluid. The less dense warm fluid will rise above the more dense colder fluid, causing the fluid to circulate. This convection current is how the thermal energy is transferred.
If a fluid's movement is restricted, then energy cannot be transferred. That is why many insulators, such as ceiling tiles, contain trapped air pockets. Wall cavities in houses are filled with fibre to prevent air from circulating and transferring thermal energy by convection. RADIATION:
Radiation, unlike convection and conduction, does not need particles at all. Radiation can travel through a vacuum. This is clearly shown by the radiation that arrives from the sun. Radiated heat energy is carried mainly by infra-red radiation, which is part of the electromagnetic spectrum.
All objects take in and give out infra-red radiation all the time. Hot objects radiate more infra-red than cold objects. The amount of radiation given out or absorbed by and object depends on its temperature and on its surface.
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