how does conduction work?
- can occur in solids, liquids and gases, but it works better and is more efficient in solids.
why?
~ in liquids and gases, according to the kinetic model of matter, their molecules are spaced further apart than solids.
~ there would be lesser collisions in liquids and gases
~ so the transfer of kinetic energy from faster moving molecules (molecules of the hotter end of the liquid/gas) to the slower moving neighbouring molecules is slower
~ in solids, their molecules are closely packed so more collisions, kinetic energy is transferred
~ heat conducts through solids the fastest; liquids and gases are poor conductors of heat.

- 2 types of conduction: molecular vibration and free electron diffusion

~ molecular vibration
Ø when heat is supplied to one end, the molecules at the hot end vibrate vigorously
Ø they collide with neighbouring molecules, making them gain kinetic energy and vibrate as well
Ø kinetic energy at the hot end is transferred to the neighbouring molecules
Ø quite a slow way

~ free electron diffusion
Ø this type of conduction only takes place in metals as only metals have free electrons
Ø when the metal is heated, the free electrons gain kinetic energy and move faster
Ø the electrons then diffuse into the cooler parts of the metal, colliding with the molecules in the cooler part of the metal
Ø much faster mechanism

~ comparing the 2 types

Molecular vibration: occurs in solids(metals and non-metals), slow process
Free electron diffusion: Occurs only in metals, faster process

this explains why metals are more capable of transferring thermal energy more quickly:
1. metals have 2 methods of conduction occurring at the same time
2. in metals, free electron diffusion is the main mechanism, which is faster

what will be observed:

~ wax melts faster along the copper rod than the wax on the glass rod
Ø copper is a conductor of heat
Ø glass is an insulator
Ø also shows that metals transfer thermal energy more quickly than non metals because of the presence of free electrons in metals

experiment~

- 2 spoons, one plastic and the other metal is put into a cup of very hot water

- equal amouts of butter is smeared on the spoons at the same level

- the butter on the metal spoon melted faster than the butter on the plastic spoons

- metals are better conductors of heat than non metal

- heat travelled through the solid through conduction

what will be observed:
~ the water at the upper end of the test tube boils quickly
~ the ice melts very slowly
Ø thermal energy transfer through conduction from the water at the top to the bottom is very slow
Ø it shows that water is a poor conductor of heat

experiment

when a matchstick is held away from a candle flame, it will not burst into flames

this is because:

- air between the matchstick and the flame is an insulator of heat