Conductors and insulators
What is a conductor?
We have already mentioned that metal is a substance that easily moves a charge of energy. A good conductor is any substance that allows a current to flow through it readily. Many metals are good electrical conductors, as is salt water.
We know that a current is more or less a flow of electrons. The reason that metals and other good conductors readily conduct electricity is because at atomic level, they easily lose their own electrons and therefore readily allow the movement of electrons to help the current flow. Two of the best metal conductors are silver and copper, both of which can be drawn into a wire.
What is an insulator?
An insulator is a substance that prevents a current from flowing. These substances are not good conductors of electricity because they do not allow electrons to move through them freely. Most plastics are excellent insulators, as is glass and carbon-based materials such as wood and paper.
You will notice that when you use wires, both at home and in a laboratory environment, that the metal wire is coated in an insulating substance, usually plastic. This coating protects you from shocking yourself on the wire as it conducts electricity. See Image 1
The human body is a good conductor of electricity. Our brain relies on sending and receiving electrical signals over our nervous system to communicate with various parts of our body. Our skin, particularly dry skin, however, is a poor conductor, which is why it takes a substantial amount of power to give us a shock. Still, you would not want to find out how much power you need to electrocute yourself.
A semiconductor is a substance that can vary its ability to conduct electricity. The conductivity of a semiconductor depends mostly on conditions such as temperature, humidity, pressure, and the presence or absence of light.
Silicon is a popular semiconductor, often used in microchips because it can alter its conducting ability with the influence of a couple of degrees change in temperature. See Image 2
Resistance is useful
When the path of electrons flows easily, as it does when the current passes through a good conductor, there is little resistance. In an insulator, however, the path of electrons does not flow easily or is blocked because there is a high resistance.
Resistance is the term scientists use to describe the ease of electrical conduction through a substance. All materials sit on a scale that measures their resistance. Good conductors provide the least resistance; insulators provide the most resistance and semiconductors sit around the middle.
Substances with a high resistance are helpful for converting electrical energy into other forms of energy, such as heat and light. The filament (thin wire) in an incandescent light bulb is made of a metal that restricts, but does not insulate the electric current. The charge builds up in the wire, which then produces light and a little heat. Household appliances such as kettles, toasters and irons do the same thing to produce heat. In a circuit, the load is just a component of resistance.
Scientists measure resistance in opposition to the flow of current. The unit of measurement is the ohm () after the German physicist Georg Ohm.