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Mr Palmer's AQA GCSE Physics Notes

	Heat Conduction The hotter an object, the more the atoms (or ions) within the object vibrate. Metals are good conductors because of the large number of free electrons contained within them. As one part of a conductor heats up, the ions gain kinetic energy and start to vibrate faster. The free electrons collide with the vibrating ions and pick up some of their kinetic energy. The free electrons then carry this energy to further parts of the conductor by colliding with other ions and electrons. The ions also pass energy to their neighbours by colliding with them. Convection Heat energy is transferred by convection in fluids (liquids and gases) in the following way: As the particles at the bottom of the fluid are heated, they gain kinetic energy and begin to vibrate faster. As the particles vibrate faster, they take up more space. Because the particles take up more space, this warmer fluid becomes less dense than the cooler fluids and begins to rise. As the warm fluid rises, it passes on its energy to the cooler fluid. As the warm fluid passes on its energy it begins to cool down. The particles start to vibrate less, they take up less space and the fluid becomes more dense. The cooler fluid sinks to the bottom, and the process repeats itself. Radiation All objects in the universe emit heat energy in the form of infra red waves (also called thermal radiation). This is the transfer of energy by electromagnetic waves. These waves are the only way heat can travel through empty space. All objects give off thermal radiation. The hotter the object is the more thermal radiation it gives off. The surface of the object affects how much infra-red radiation it gives off in the following ways: A light, shiny surface gives off less radiation and is a good reflector of radiation. A dark, matt surface gives off more radiation and is a good absorber of radiation. Because of these properties, a light, shiny object will change temperature slowly. A dark, matt object will change temperature quickly. Insulation ^{Heat is lost in the average home in the following ways} Draughts transfer heat by convection. Draughts can be reduced by fitting the house with draught-proof strips, laying thick carpet and fitted curtains. Older homes have an air cavity between the inner wall and the outside wall. This reduces heat loss by conduction as air is a good insulator.	Navigation Physics P1 Topics Heat Energy Electricity Power Electromagnetic Spectrum Nuclear Radiation Origins of the Universe Physics P2 Topics Motion Forces Energy Static Electricity Current Electricity Mains Electricity Momentum Nuclear Physics Other Mathematics for Physics