Conductors, semi conductors, and insulators are important when dealing with electricity. An electric conductor is a material that can carry an electric current. When atoms combine to form a solid, electrons are often liberated and can move with ease through the material. The best conductors are metals because the electrons can move freely through the material, carrying the current. The best conductors have very little resistance.
Resistance is measured by the ohm.
It occurs as the electrons move and they strike each other and the atoms, losing energy. When this happens, more energy is needed to keep the current flowing to push the electrons through the material. This extra energy is the voltage. The energy lost when the electron hits another electron or an atom causes the material to heat up, which is why light bulbs often become very hot. An insulator is a material that does not conduct electricity well because it holds its electrons very tightly.