Transfer of Thermal Heat
Conduction:
This is the transmission of heat from a higher temperature region to a lower temperature region without the movement of molecules from one place to another, however it is transmitted by the vibration of molecules.
As a material receives heat energy, the molecules close to the heat supply begin to vibrate. The increase in heat of a body is displayed as an increase in the kinetic energy that the molecules possess. The vibrating molecules pass on their kinetic energy by 'bumping' into their neighbouring molecules and causing them to vibrate more vigorously. The heat is passed on in the solid in this way. Note that there is no flow of the molecules themselves.
All metals are good conductors of heat compared to other materials. This is because metals contain free electrons which move independently throughout the metal. These electrons move faster when the metal is heated and diffuse into the cooler parts of the metal and then transfer their kinetic energy.
Materials such as plastic, wood and glass are usually bad conductors of heat. Trapped air acts as a very good insulator. Expanded polystyrene, fibre glass and thick clothes contain lots of trapped air and make excellent insulators.
Water is a poor conductor of heat.
Conduction is slower in liquids and gases because the molecules are further apart and not as likely to collide with each other to pass on their kinetic energy as in solids.
See the video to determine the conductivity of different types of metals.
Convection
Convection currents are a flow of liquid or gas caused by a change in density, in which the whole medium moves and carries heat energy with it. They occur when a liquid or gas rise above a source of heat. The fluid in close contact with the heat source expands as it heats up. It expands because the molecules are now moving faster with more kinetic energy and push each other further apart. The expanded fluid is now less dense than the surrounding water and rises above the cooler and more dense fluid. The cooler fluid sinks to the bottom and a convection current is set up.
Land and sea breezes come about as a result of convection currents.
Sea breeze
In sunshine, the land warms up more quickly than the sea
The wire over the land becomes warmer than the that over the sea
The warmer air over the land rises and the cooler air above the sea moves inland, forming a convection current or breeze blowing in from the sea - this is called a sea breeze.
Land breeze
At night, the land cools more quickly than the sea
The warmer air is now
This air rises and the cooler air moves from the land towards the sea - this is called a land breeze.
Radiation
This the transmission of heat without the movement of particles. Radiation can travel though a vacuum, i.e. it does not require a material medium. Most life on earth depends upon energy from the sun, and this comes in the form of visible and invisible radiation that travels through about 150 million km (93 million miles) of (mostly) empty space, or a vacuum, to reach the earth.
Radiation that falls on an object is partly absorbed, partly reflected and partly transmitted. Dull, black surfaces are better at absorbing radiation than white, shiny surfaces. Good absorbers are also good emitters.
Poor absorbers such as white, shiny surfaces are also poor emitters.
Conduction and convection both require material mediums. Conduction is the transfer of atomic/molecular vibrations. Convection is the motion of the fluid itself, carrying heat with it. Thus, neither of these can occur in a vacuum.