A resistor is a passive electrical component that limits or regulates the flow of electrical current through a circuit. The current is calculated via Ohm's law: V = IR. For a given voltage, a resistor with a larger value will produce less current than a resistor with a smaller value. Some amount of resistance is always present in any practical conductor. Resistance value, tolerance, and sometimes even temperature coefficient can be determined by reading the resistor color code, indicated by a series of colored bands on the side of the resistor.