Editing Alternating current (section)

==== Coaxial cables ====
[[Coaxial cable]]s are commonly used at [[Audio frequency|audio frequencies]] and above for convenience. A coaxial cable has a conductive wire inside a conductive tube, separated by a [[dielectric]] layer. The current flowing on the surface of the inner conductor is equal and opposite to the current flowing on the inner surface of the outer tube. The electromagnetic field is thus completely contained within the tube, and (ideally) no energy is lost to radiation or coupling outside the tube. Coaxial cables have acceptably small losses for frequencies up to about 5&nbsp;GHz. For [[microwave]] frequencies greater than 5&nbsp;GHz, the losses (due mainly to the dielectric separating the inner and outer tubes being a non-ideal insulator) become too large, making [[Waveguide (electromagnetism)|waveguides]] a more efficient medium for transmitting energy. Coaxial cables often use a perforated dielectric layer to separate the inner and outer conductors in order to minimize the power dissipated by the dielectric.