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12 Cards in this Set

  • Front
  • Back
Why are metals good conductors?
Metals contain lots of free electrons. These electrons move about at random positions inside the metal and hold the positive metal ions in their fixed positions. The free electrons collide with each other and with the positive ions.

When a metal rod is heated on one end, the free electrons at that end get hot and gain kinetic energy, moving faster. They diffuse and collide with other free electrons and ions in the cooler parts of the metal, transferring kinetic energy to them.
Why are non-metals usually worse conductors than metals?
All the electrons are held in the atoms so energy transfer only takes place because atoms vibrate and shake each other.
What is convection?
When a hot fluid (liquid or gas) goes up and a cold fluid is drawn down.
How do hot water tanks work?
Hot water from the boiler rises and flows into the tank where it rises to the top. The cold water is brought back down to the boiler where it is heated.
What are sea breezes?
On a sunny day the ground heats up faster than the sea, so the air above the ground warms up and rises. This causes cold air from above the sea to take the place of the warm air.
Why do fluids rise when heated?
They become less dense when heated. The particles move about more and they move apart, taking up more space so the density decreases since the same mass occupies a bigger volume.
Why does evaporation have a cooling effect?
The faster particles, which have more kinetic energy, break away from the attraction of the other particles at the surface and escape the liquid. The liquid is cooler because the average kinetic energy of the particles left has decreased.
How do greenhouses work?
Short-wavelength infrared radiation (and light) from the Sun pass through the class to warm objects inside it. The infrared radiation from the warm objects has longer wavelengths that can't pass through the glass so they are reflected back.
Which surfaces are the best emitters of radiation and why?
Dark, matt surfaces are better at emitting infrared radiation than light, shiny surfaces.
Which surfaces are the best absorbers and reflectors of radiation?
Black surfaces absorb more radiation than white surfaces. A matt surfaces absorbs more radiation than a shiny one since a matt surface has lots of cavities so the radiation reflected from the matt surfaces hits the surface again.

Light, shiny surfaces reflect more infrared radiation than dark, matt surfaces.
How do vacuum flasks work?
There is a vacuum between the two walls of the container which cuts out energy transfer by conduction and convection between the walls.

Glass is a poor conductor so there is little energy transfer by conduction in the glass.

The glass surfaces are silvery to reduce radiation from the outer wall.

The plastic cap stops cooling by evaporation since it stops vapour loss from the flash. Any energy transfer by conduction is cut down because the cap is made from plastic. The plastic support spring is also made from plastic.
What factors affect the rate of energy transfer?
The bigger the temperature difference between an object and its surroundings, the faster the rate at which energy is transferred.

The material the object is made from.

The object's mass.

The object's volume and surface area.

The nature of the surface that is in contact with the object.