Electronics Basics: Resistance
In the electronics world, resistance is not futile. In fact, resistance can be very useful. Without resistance, electronics would not be possible. Electronics is all about manipulating the flow of current, and one of the most basic ways to manipulate current is to reduce it through resistance. Without resistance, current would flow unregulated and there would be no way to coax it into doing useful work.
A conductor is a material that allows current to flow, and an insulator is a material that doesn't. Good conductors allow current to flow with abandon, without impediments. Examples of good conductors include the metals copper and aluminum. Carbon is also an excellent conductor.
Good insulators, on the other hand, erect solid walls that completely block current. Examples of good insulators include glass, Teflon, and plastic. The key factor that determines whether a material is a conductor or an insulator is how readily its atoms give up electrons to move charge along.
Most atoms are very possessive of their electrons, and are therefore good insulators. But some atoms don't have a strong hold on their outermost electrons. Those atoms are good conductors.
If a conductor and an insulator are mixed together, the result is a compound that conducts current, but not very well. Such a compound has resistance — that is, it resists the flow of current. The degree to which the compound resists current depends on the exact mix of elements that make up the compound.
For example, a conducting material such as carbon might be mixed with an insulating material such as ceramic. If the mix is mostly carbon, the overall resistance of the mixture will be low. If the mix is mostly ceramic, the overall resistance will be high.
The truth is that all materials have some resistance. Even the best conductors have a small but measurable amount of resistance. The only exceptions are certain materials called superconductors that, when chilled to unbelievably low temperatures, conduct with 100 percent efficiency.