Energy Transfer By Heating Flashcards
Energy is………….by conduction and convection
Transferred
What are the best conductors of energy
Metals
Why are metals good conductors
Because metals contain lots of free electrons which move about at random inside the metal
Describe what happens when a metal rod is heated at one end
-The free electrons at the hot end gain kinetic energy and move faster
-These electrons diffuse (spread out) and collide with other free electrons and ions in the cooler parts of the metal
-As a result, they transfer kinetic energy to these electrons and ions
So energy is transferred from the hot end of the rod to the colder end
Where are the electrons held in a non metallic solid
In the atoms
How does energy transfer take place in non metallic solids
Energy transfer only takes place because the atoms vibrate and shake each other.
This is much less effective than energy transfer by free electrons
What materials are good insulators
Wool and fibreglass
Why are wool and fibre glass good insulators
Because they contain air trapped between the fibres. Trapped air is a good insulator
What do we use materials such as fibreglass for
Insulating lofts and hot water piping
When does convection occur
When particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy
What is transferred by convection
Heat energy is transferred from hot places to cooler places by convection.
Why do liquids and gases expand when they are heated
Because the particles in liquids and gases move faster when they are heated than when they are cold.
As a result. The particles take up more volume.
This is because the gap between particles widens, while the particles themselves stay the same size
Describe what happens during convection
The liquid or gas in hot areas is Less dense than the liquid or gas in cold areas, so it rises into the cold areas.
The denser co,d liquid or gas falls into the warmer areas.
In this way, convection currents that transfer heat from place to place are set up
Energy may be ………… By evaporation and condensation
Transferred
What happens during evaporation
The particles in a liquid have different energies.
Some will have enough energy to escape from the liquid and become a gas
Why does evaporation have a cooling effect
The remaining particles in the liquid have a lower average kinetic energy than before, so the liquid cools down as evaporation happens
