Also known as an inductor, a coil is a component used in some electronic circuits and most electric motors. The electronic component version of a coil is simply a coil of wire wrapped around some ferrous material such as iron. Besides being used to make transformers, coils are often used in a variety of circuits because of their unique properties for handling voltage and current. Similar in some ways to a capacitor, a coil stores an electric charge, however they do it by building a magnetic field rather than the battery-like charging operation of a capacitor. When the electric current is removed from a coil the magnetic field collapses and produces additional current flow. When alternating current passes through a coil its field is constantly collapsing and being rebuilt with each cycle of AC. The time it takes for this to occur will have a coil react differently to different frequencies, which makes them have specific properties that are useful in audio & radio frequency circuits (among other things). A coil will present a higher resistance to current flow at higher frequencies and virtually no resistance to DC (notice this is opposite behavior from a capacitor). Coils are also very easy to “tune” because they can be constructed so a simple screwdriver can move the ferrous material in or out of the coil of wire, which significantly changes the charging properties.