Presentation on theme: "Conduction in Non-Metals Every atom is physically bonded to its neighbours in some way. If heat energy is supplied to one part of a solid, the atoms vibrate."— Presentation transcript:
Conduction in Non-Metals Every atom is physically bonded to its neighbours in some way. If heat energy is supplied to one part of a solid, the atoms vibrate faster. As they vibrate more, the bonds between atoms are shaken more. This passes vibrations on to the next atom, and so on: Eventually the energy spreads throughout the solid. The overall temperature has increased.
Conduction in Metals All metals are good conductors of electricity. For a similar reason, they are also good conductors of heat. electricity In metals, not only do the atoms vibrate more when heated, but the free electrons charge around more as well. These transfer the energy much faster than just vibrations in bonds.
Conduction Summary Conduction happens mainly in solids. All atoms vibrate, but vibrate more when heated. Heat spreads by conduction when atoms increase their vibrations, and pass this energy on to those nearby. In metals, free electrons carry the heat energy faster than the atomic vibrations......and transfer it by colliding with other electrons and atoms. Because of this, metals are the best conductors of heat energy.
Convection Perhaps the first thing that most people say is "heat rises". Whilst not wrong, what you should say is "hot air rises" or "hot water rises". Anything fluid - that is gases or liquids - will tend to change density with changes in temperature. For example, if heated, air decreases in density. The surrounding air is cooler and denser. This makes it heavier, so it falls beneath the hot air, forcing it upwards.
Convection in rooms In cooler countries, many houses have radiators to heat their rooms. This is a bad name for them - as they give off heat mainly by convection! The convector heater warms the air in contact with it. This becomes less dense, and rises. The ceiling forces this air to circulate as shown, warming the air around it. Finally, when the air has cooled, it falls downwards, completing the cycle.
Convection Everywhere Convection currents occur wherever fluids are being heated. Here are some more examples: Water in kettles Soup in saucepans Water in a hot water tank Convection even occurs in the sun!
Convection Summary Convection occurs in gases and liquids. Hot fluids rise, cold fluids fall. Convection currents occur because heat is lost from the rising fluid, cooling it down. The whole fluid will rise in temperature as a result of mixing caused by convection currents.
Radiation As you may have read elsewhere, heat energy can be transferred by radiation. This is infra red waves, a type of light. elsewhereinfra red waves Just like light, infra red waves can travel in a vacuum. This is why we can feel the sun's warmth - this heat has travelled 92 million miles to reach us!
Radiation Heat radiation has the useful property of being able to travel in all directions - unlike in convection. convection Heating in bathrooms is often provided by radiant heaters, which safely reflect heat from a bar that is hot due to its electrical resistance: The orange glow of the bar is visible light. Remember: most of the radiation coming off it is infra red... heat. But like light, it travels in straight lines.infra red
Radiation Summary Heat radiation consists of infra red waves. These travel at the speed of light, in straight lines. Heat radiation can go in any direction, even through a vacuum. Heat reaches us from the Sun by IR radiation. infra red waves