From Ice Age Farmer Wiki
A resistor is an electrical component used to provide electrical resistance in a circuit - that is, it impedes the flow of current. Resistors are usually made of carbon and marked with coloured bands which indicate the level of resistance they provide (measured in ohms). Another kind of resistor is a potentiometer, in which the resistance is adjustable.
Some resistors are larger than others. The larger ones can have more power flowing through them.