Karteikarten
Heat Transfer
Karten in diesem Stapel (23)
- 1Heat TransferPhysics 1a 1.1 - 1.5
- 2How do thermal detection cameras work?The hotter an object is, the more thermal radiation it emits.
- 3How do you detect thermal radiation?See page 24 for diagram.
- 4What is the electromagnetic spectrum?Radio waves, microwaves, infra-red radiation and visible light are all part of the electromagnetic spectrum, along with ultraviolet rays and X-rays. They are magnetic and electrical waves which travel through space.
- 5How does the greenhouse effect work?In a greenhouse, shorter wavelength radiation from the sun can pass through the glass, however longer wavelength thermal radiation is trapped inside by the glass - the Earth's atmosphere acts as a greenhouse for the planet.
- 6How is the greenhouse effect affecting our planet?Gases in the atmosphere trap the thermal radiation given off from the Earth making it warmer. However this is causing the polar ice caps to melt and so the sea level will rise. Cutting back on the use of fossil fuels will also help to reduce the greenhouse gases which trap the energy.
- 7Which surfaces are the best absorbers of radiation?A darker surface absorbs radiation better than a light one, a matt surface also helps to absorb radiation as it has lots of cavities. The incident of radiation is scattered and absorbed within these.
- 8What makes a good conductor?Metals conduct heat better than non-metals, of which copper is a better conductor of heat than steel. Wood conducts heat better than glass.
- 9How do metals conduct heat?They contain lots of delocalised (free) electrons, they move about at random within a metal holding the positive ions together, colliding with each other. When metal is heated, they gain kinetic energy quickly and begin moving about.
- 10How is energy transferred through a metal?The free electrons diffuse and collide with other delocalised electrons and ions in the cooler parts of the metal. As a result, the kinetic energy is passed on to these electrons and ions.
- 11How is heat transferred in a non-metal?All of the electrons are held in place within the atoms, therefore energy transfers only take place because the atoms vibrate and shake each other, this is a much less efficient form of energy transfer.
- 12Where and when can convection take place?Only in liquids and gases (i.e. fluids), and due to circulation.
- 13How does convection work?The warmer fluid rises because it is less dense until it cools, then it is displaced by the cooler fluid as this is more dense causing a convection current. Fluids expand when heated which makes them less dense.
- 14Give two examples of convection currents in practice.1) Hot water boilers.
2) Sea breezes. - 15Explain how one of these examples work.1) Hot water from the boiler rises and flows into the tank above, the water in your tap will be taken from the top.
2) On hot days, the land heats up faster than the sea so the air above the ground heats up and rises, cooler air from the sea flows in to replace it. - 16Why are car radiators painted black?Dark colours absorb radiation better.
- 17How does the cooling system of a car engine work?It transfers thermal energy from the engine to a radiator, this is flat so it has a large surface area which increases heat loss through convection in the air and through radiation. A cooling fan also helps to regulate air flow.
- 18How does a vacuum flask work?The liquid is found within a double-walled glass container, the vacuum between the two walls of the container cuts out heat transfer by conduction and convection between the walls. Glass is a poor conductor, and the surface is silvery to reduce radiation from the outer wall.
- 19List the four ways that heat loss is reduced at home.1) Loft insulation.
2) Aluminium foil insulation.
3) Double glazed windows.
4) Cavity wall insulation. - 20How does loft insulation prevent heat loss through the roof of a building?Air between the fibres helps to reduce heat loss by convection, and heat rises.
- 21How does aluminium foil insulation protect against heat loss?By placing the foil between a radiator panel and the wall, all heat radiation is reflected away from the wall and back into the house.
- 22How does double glazing prevent heat loss?The dry air or vacuum between the two panes cuts down heat conduction and heat transfer by convection as well.
- 23How does cavity wall insulation reduce heat loss from the home?We place insulation between the two layers of brick which make up the walls of the house.