Convection

Convection is the transfer of thermal energy by means of
currents in a fluid.

It only takes place

in liquids and

gases but not in

solids as convection

involves the movement

of fluids which carry

thermal energy while

thermal energy is

transferred from one

particle to another

through vibrations.

Does conduction take place in Liquids & Gases?

Conduction does take place in liquids and gases but they are inefficient.The particles are spaced further apart than solids so collisions between particles are less frequent.Thus, the transfer of heat from molecule to molecule is slower. This explains why liquids and air are poor conductors of heat.

Question
All liquids are poor conductors of heat except molten mercury. Why?

Answer
Molten mercury is a metal in liquid form and it has properties of metals. For example, it has free and mobile electrons, which is a property of metals. Therefore, it is a good conductor of heat.

why are metals good conductors of heat?

All solids are made up of atoms and molecules. However, metals contain free electrons which move randomly between the atoms and molecules.

One mechnism for conduction is atomic or molecular vibrations. When thermal energy is supplied to one end of a rod, the atoms or molecules at the hot end will vibrate vigrously. The particles will collide with neighbouring particles, causing them to vibrate as well. Thus, the kinetic energy is transferred from particle to particle.This is how the heat is transferred from the hot end of the rod to the cold end. This mechanism takes place in both metals and non-metals.

The other mechanism for conduction is free electron diffusion which only takes place in metals. When a metal rod is heated, the free electrons gain kinetic energy and they move faster. These electrons then diffuse or spread into the cooler parts of the rod. Thus, they collide with the particles in the cooler parts of the metal and transfer their kinetic energy to them.Thus, this explains why metals are capable of transferring thermal energy much faster than insulators.

Conduction

Conduction:

It is the process of thermal energy tansfer without any flow the material medium.

For example, look at the picture below. One end of the rod is placed over a candle. Over time, the whole rod is hot as heat is transferred from a hotter region (end of rod above flame) to a cooler region (other end of rod not above flame) by conduction.

Different materials conduct heat at different rates. In general, metals such as copper,silver and steel are good conductors of heat. Non-metals like glass, distilled water and water are insulators of heat.

Transfer of Thermal Energy

Thermal Energy:

It always flows form a region of higher
temperature to a region of lower temperature.

3 process of how thermal energy is transferred:
Conduction Convention Radiation

video on Convection

Hi! i found this video that shows various experiments on convection. However, i cannot seem to be able to upload it on my blog so this is the URL of the video :
http://www.youtube.com/watch?v=HIYCR7gXXFo&feature=related