lectricity is usually transmitted over copper wires (though any metal could be used). The phone system uses copper wire to transmit voice and data. Ethernet networks also use copper wire to connect devices. Electricity transmitted on a copper wire faces resistance from the copper and this resistance will distort the signal. This distortion, ornoise reduces the maximum capacity of the wire according to the Nyquist theorem. Since all telecommunications technology over copper wires today uses direct current (DC), the noise and attenuation caused by copper's resistance to electricity is a serious limitation. Total distances for direct current communication is usually measured in thousands of feet, not miles. This weakening of the electric current does several things to the data carried by the electric signal. First, the farther the signal travels, the weaker it gets because some of the electricity is turned into heat by the resistance of the copper. This imposes a limit to how far a signal can be transmitted. Second, the copper wire can cause what is called attenuation. Parts of the signal simply get chopped off and are gone, changing the signal and causing information to be lost. Still, for short range communication, copper wire is usually the best choice.