Several resistors are shown. Resistors impede the flow of current by a calibrated amount, usually coded on the resistor in colored bands, or simply listed as a value in ohms. A resistor of 1 ohm will have 1 ampere of current flowing through for each volt established across it. A resistor (or anything else) will dissapate 1 watt (mostly heat) for each ampere of current through it times each volt established across it.