Thermal conduction is a type of heat transfer in which heat is transferred through the body from areas of higher temperature to areas of lower temperature. The thermal conductivity of substances is different. There are good and bad conductors of heat.
Metals are good conductors of heat.
Heat conduction takes place in a body only when areas of different temperatures are present. The heat is always transferred from areas of higher temperature to areas of lower temperature. If a body is left to its own, the temperature will gradually equalize. The heat transmitted through a body depends of the:
- Substance of which the body is made,
- The cross-sectional area of the body,
- Temperature difference,
- Length (dimensions) of the body,
- Time.
The thermal conductivity is a material constant. Depending on the value of these material constants, a distinction is made between good and bad heat conductors.
All metals, especially silver, copper, gold and aluminum, are good heat conductors.
Almost all plastics, wood, water, glass and, above all, air are poor heat conductors.
Water is a poor conductor of heat.
Heat conduction can also take place from one substance to another. The heat then passes from one substance to another. This is known as heat transfer. Heat is transferred, for example, from the surface of an immersion heater to the surrounding water. Another example is the transfer of heat from the bottom of a saucepan to the food in it.
- Have you ever taken a spoon out of a mug of hot cocoa or tea or some other hot drink?
- Did you find that the spoon was too hot to hold, so that you had to drop it?
- Did you burn your fingers?
If you have never done this, don’t try it now.
But if you have done this, then you found out the hard way that heat can travel through some solid materials, such as metals. When heat travels in this way, we say that the heat is conducted. In the hot drink, the heat is conducted from the liquid into the metal spoon.
- Why was the handle of the spoon so hot?
Atoms in the bowl of the spoon move faster and bump harder into each other as they heat up. The faster the atoms vibrate the hotter the spoon becomes. The atoms in the lower part of the spoon then bump into the metal atoms a little farther up the spoon. These atoms then bump against their neighbors even farther up and start them vibrating. Soon, all the atoms in the spoon are vibrating faster.
When the handle of the spoon is cold, the atoms in the metal vibrate slowly.
Why do metals conduct heat and electricity so well?
Metals are the best conductors of heat and electricity because they contain an abundance of free electrons. It is known that the positive nucleus binds the negative electrons to the atom. The force with which this is achieved is called Coulomb force.
The Coulomb force becomes weaker with increasing distance.
Thus we can conclude that the force that the electrons occupy increases when the closings become weaker, and of course weakest when the electrons are drawn into the outermost or so-called valence shell.
These electrons are so weakly attracted that they manage to escape and free themselves from the atom.
They are therefore called free electrons.
What is responsible for a metal's tendency to lose its valence electrons is its large atomic size and its own lack of valence electrons. Each metal atom produces one or two free electrons, and a piece of any metal contains a huge number of atoms. Sheet metal is full of free electrons, and it is these free electrons that propagate heat and the current flowing through it.
How Free Electrons Propagate Electricity and Heat
For example, if we connect a copper wire to a battery, the positive pole attracts the negative free electrons. The sudden force exerted by the electric field makes them spin and crash violently at tremendous speed. A domino effect follows.
In the same way, heat is conducted through a metal. A source of thermal energy is nothing more than a source of kinetic energy. When we apply a source of heat to a material, it transfers kinetic energy to the atoms of the material. This kinetic energy energetically puts the atoms in their place. The higher the heat, the stronger the tremor.
Ionic compounds also conduct heat when ions wobble in their positions. Ionic compounds, however, are characterized by a highly symmetrical geometric arrangement or structure. They wobble, but their movement is severely limited by this structure.
Pure metals, on the other hand, are superlative conductors because their atoms are restricted by their structure, but their electrons are not. They are free. The electrons move randomly when the source gives them kinetic energy. They then collide with neighbouring electrons and transfer their kinetic energy during the process. Collisions emulate a domino effect and heat is transferred from the hot area, the area closest to the source, to the cold area.
Social Plugin