The word copper comes from the Latin word ‘cuprum’, which means ‘ore of Cyprus’. This is why the chemical symbol for copper is Cu. Copper has many extremely useful properties, including:
- good electrical conductivity
- good thermal conductivity
- corrosion resistance
It is also:
- easy to alloy
- easily joined
See below for more information on each of these properties, and how they benefit us in our daily lives.
Good Electrical Conductivity
Copper has the best electrical conductivity of any metal, except silver.
A good electrical conductivity is the same as a small electrical resistance. An electric current will flow through all metals, however they still have some resistance, meaning the current needs to be pushed (by a battery) in order to keep flowing. The bigger the resistance, the harder we have to push (and the smaller the current is). Current flows easily through copper thanks to its small electrical resistance, without much loss of energy. This is why copper wires are used in mains cables in houses and underground (although overhead cables tend be aluminium because it is less dense). However, where size rather than weight is important, copper is the best choice. Thick copper strip is used for lightning conductors on tall buildings like church spires. The copper strip has to be thick so that it can carry a large current without melting.
Copper wire can be wound into a coil. The coil will produce a magnetic field and, being made of copper, won’t waste much electrical energy. Copper coils can be found in:
How copper conducts
Copper is a metal made up of copper atoms closely packed together.
If we could look closely enough, we would see that there are electrons moving about between the copper atoms.
Each copper atom has lost one electron and become a positive ion. So copper is a lattice of positive copper ions with free electrons moving between them. (The electrons are a bit like the particles of a gas that is free to move within the surfaces of the wire).
The electrons can move freely through the metal. For this reason, they are known as free electrons. They are also known as conduction electrons, because they help copper to be a good conductor of heat and electricity.
The copper ions are vibrating (see Figure 1). Notice that they vibrate around the same place whereas the electrons can move through the lattice. This is very important when we connect the wire to a battery.
We can connect a copper wire to a battery and a switch. Normally, the free electrons move about randomly in the metal. When we close the switch, an electric current flows. Now the free electrons flow through the wire (Figure 2) they are moving from left to right (and still move randomly as well).
Electrons have a negative charge. They are attracted to the positive end of the battery. The free electrons move through the copper, flowing from the negative to positive terminal of the battery (note that they flow in the opposite direction to conventional current; this is because they have a negative charge).
The copper ions in the wire vibrate. Sometimes an ion blocks the path of a moving electron. The electron collides with the ion and bounces off it. This slows down the electron. Some of its energy has been transferred to the ion, which vibrates faster.
In this way, energy is transferred from the moving electrons to the copper ions. The copper gets hotter. This explains why:
- metals have electrical resistance.
- metals get hot when a current flows through them.
Good Thermal Conductivity
Copper is a good conductor of heat. This means that if you heat one end of a piece of copper, the other end will quickly reach the same temperature. Most metals are pretty good conductors; however, apart from silver, copper is the best.
It is used in many heating applications because it doesn’t corrode and has a high melting point. The only other material that has similar resistance to corrosion is stainless steel. However, its thermal conductivity is 30 times worse than that of copper.