Conduction

From the video, it can be seen that heat transfer, conduction (or heat conduction) is the transfer of thermal energy between neighboring molecules in a substance due to a temperature gradient. It always takes place from a region of higher temperature to a region of lower temperature, and acts to equalize temperature differences.

Fourier's law (aka Law of Heat Conduction)

It states that the time rate of heat transfer through a material is proportional to the negative gradient in the temperature and to the area at right angles, to that gradient, through which the heat is flowing.

The differential form of Fourier's Law of thermal conduction shows that the local heat flux (meaning: the amount of energy flow through a particular surface per unit area per unit time), , is proportional to the thermal conductivity, k, times the negative local temperature gradient, .

where (including the SI units)
is the local heat flux, [W·m−2]
is the material's conductivity, [W·m−1·K−1],
is the temperature gradient, [K·m−1].

The thermal conductivity, k, is often treated as a constant, though this is not always true. While the thermal conductivity of a material generally varies with temperature, the variation can be small over a significant range of temperatures for some common materials.

For many simple applications, Fourier's law is used in its one-dimensional form. In the x-direction,

Applications of Conduction

Cooking utensils - thermal energy is required to be transferred quickly through these good conductors of heat (metal) so as to warm up the food fast.

However, on a closer look, it can be seen that these utensils also have handles. These handles are usually made of insulators (bad conductors) of heat so as to prevent so much heat from passing to the handle and thus might cause the user to suffer serious burns.

For example, a spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon. Conduction is most effective in solids-but it can happen in fluids.

*Fun fact: Have you ever noticed that metals tend to feel cold? Believe it or not, they are not colder! They only feel colder because they conduct heat away from your hand. You perceive the heat that is leaving your hand as cold.

Experiment about Conduction

In this experiment, conduction is explored by testing the conductivity of three kitchen utensils made of plastic, wood and metal. This is to determine which utensil heats the quickest. Metal conducts heat at least 500 times better than wood. The relation between heat conductivities for wood and plastic depends on the type of plastic, but the values are similar.

Procedure
1. Press a small piece of warm candle wax from Part I into the handle of each of the three spoons (see diagram). Push the quarters into the wax so that they are attached to the spoons.
2. Fill the beaker with 300 mL water and place the beaker on a hot plate.
3. Place the three spoons in the water so that the quarters come out of the top of the beaker.
4. Turn on the hot plate and allow the water to warm. Observe the quarters and note the order in which they fall from the spoons.

The wax and quarters on the metal spoon should fall off first followed by the wood amd plastic spoon. This shows that thermal energy flows through the material of the sppons without any flow of the material itself. Such a transfer of thermal energy without any movement of the material medium is known as conduction. Different maerials conduct heat at different rates. Since the length of unmelted wax is shortest for metal and longest for wood and plastic, it can be proven that metals are good conductors of heat and wood as well as plastic are insulators.

It works this way because all solids (both metals and non-metals) are made up of tiny particles called atoms and molecules. The difference between metals and non-metals is that metails contain many free electrons which move randomly between the atoms or molecules, while non-metals do not have such free electrons.