Thermal Energy Flashcards
What process happens in poor conductors?
Neighbouring atoms transferring thermal energy to each other due to their vibrations. This is a slow process.
What processes happen in good conductors?
Neighbouring atoms transferring thermal energy to each other due to their vibrations and delocalised electrons collide with ions transferring thermal energy to each other due to their vibrations. The second process is a very fast process.
What are good conductors of heat?
Metals are good conductors of heat, but non-metals and gases are poor conductors of heat, an example being trapped air - a cheap and effective insulator
What is the correlation between heat and energy?
Heat causes there to be more energy in particles; this is the reason that the atoms vibrate in hot solids.
What is the correlation between delocalised electrons and conductivity?
The more delocalised electrons in a metal, the more conductive the metal will be. This is because vibrations can be passed on faster.
What is the correlation between density and conductivity?
The more dense a metal is, the closer the particles are, therefore vibrations are more easily transferred due to a short distance between the particles.
What is convection?
Convection is the transfer of heat through fluids (liquids and gases) by the upward movement of warmer, less dense regions of fluid.
What happens in a convection current?
The heat source transfers thermal energy to the air, when then expands less dense and rises. The air that was heated up is now away from the heat source, and cools down, contracts, becomes less dense and falls. When the hot air rises, cold air rushes in the fill the space. The whole cycle is then repeated.
What happens when a fluid is exposed to heat?
A fluid will expand, becomes less dense and rise.
What is thermal radiation?
Thermal radiation is the transfer of thermal energy via infrared waves which means it can travel through a vacuum.
Can all objects emit and absorb thermal radiation?
Yes. However, dull black objects are the best absorbers and emitters.
How do we know whether an object is an emitter or an absorber?
If the room is cooler than the object, the object will emit. If the room is hotter than the object, the object will absorb.
How can conduction through walls be reduced?
The two layered wall construction with the cavity filled with insulation panels helps to reduce heat loss by conduction, convection and even radiation. Conduction is prevented by the trapped air, and convection currents are prevented from circulating by glass fibre insulating wall in the cavity. Radiation can be prevented by having shiny silver surfaces.
How can conduction be reduced in windows?
Double glazing helps to stop heat escaping from the home. Conduction is prevented by the trapped air.
How does roof insulation stop heat loss?
Roof insulation in modern houses uses similar panels to those used in wall cavities, trapping a thick layer of air. This takes advantage of the poor conduction property of air, whilst also preventing convection currents circulating. Again, reflective foil is used to reduce radiation heat loss.
