Collection Screen Savers Win Wallpaper Mac Wallpaper Movie Gallery Resistance Resistance refers to the property of a substance that impedes the flow of electric current. Some substances resist current flow more than others. If a substance offers very high resistance to current flow it is called an insulator. If its resistance to current flow is very low, it is called a conductor. Resistivity refers to the ability of substances to resist current flow.
Good conductors have low resistivity and insulators have high resistivity.
Resistance at the Molecular Level Resistance to current flow occurs at the molecular level of substances. For example, a metal conductor, such as copper, consists of atoms having free electrons in their outer most shells. These free electrons ordinarily move randomly from one atom to another. However, if a potential difference, also called voltage, is applied across the conductor, such as with a battery, free electrons flow from the negative to the positive terminals of the battery. Electric current refers to the rate of flow of electric charge, which causes free electrons to flow.