Models of Energy Transfer
The kinetic particle model is useful in describing heat transfer in materials. Heat energy always moves from a region of high temperature to a region of low temperature. Conduction, convection and radiation are methods by which we observe heat transfer.
Conduction
Conduction is the transfer of heat energy through a solid. There is no net movement of particles. The particles in the hottest part of a material, vibrate further from their usual positions. They transfer energy through collisions with lower-energy particles. The substance reaches thermal equilibrium when the average kinetic energy of all the particles becomes the same.
Thermal conductivity
Different materials have different conducting properties. Thermal conductivity measures the rate at which thermal energy can flow through a substance.
Convection
Convection is the transfer of heat caused by the movement of particles. Convection occurs in liquids and gases where particles are free to move. Liquids and gases that are warmer will expand and become less dense than those which are cooler. The flow of particles from warmer to cooler areas produces convection currents. Convection currents can occur in air masses in the atmosphere, in ocean currents and in hot water systems in the home.
Radiation
Radiation is a form of energy transfer that does not require particles – It requires no medium. Radiation refers to all parts of the electromagnetic spectrum – radio, microwaves, infrared, visible, ultaviolet, X-rays, gamma rays. Radiation is the transfer of heat through a vacuum by the propagation of electromagnetic radiation. Electromagnetic radiation travels at the speed of light and when it strikes a surface it can be reflected, transmitted or absorbed. Electromagnetic radiation that is absorbed will cause a rise in temperature. Electromagnetic radiation is emitted by all objects that are above 0K or −273°C. Higher temperatures will result in higher frequencies of radiation being emitted.