# The Science Guys

### May 2002

Does the electricity flowing in wires wear out the wires, that is, do the wires lose mass after electricity flows through them?

Nearly everything we know about in our everyday life tends to wear out. It seems natural for someone to wonder if the wires that carry electricity wear out as electricity flows through them.

To answer this, first think of a wire as a conduit that has something flowing through it. If the conduit is absolutely full, whenever a quantity of material flows in one end an equal amount of material must flow out the other end. Such is the case with electricity. The material flowing in wires carrying electricity is electrons and when a given number of electrons flow into a wire, an equal number must flow out. The wire is simply a pathway for the electrons to travel.

Wires are made of metals, which are conductors. Conductors have some electrons that are rather free to move. Electric current (electricity) is a flow or movement of these electrons through the conductor. The amount of current flowing is given in units called amperes. These electrons are forced to move by an electrical potential difference between two points in the wire. This potential difference can be created by a battery, generator, solar cell, or similar device and is expressed in units called volts.

Consider a wire connected to the terminals of a battery with a given potential difference (voltage). The potential difference created by the battery causes electrons to move in one end of the wire and out the other end in equal numbers. Imagine a pipe the diameter of a marble filled with marbles. If you push a marble in one end, then a marble must exit out the other end. Such is the case with a wire. As electrons move in one end of the wire, an equal number move out the other end. Nothing is created or lost in the wire during normal current flow. There is just as much wire after electricity flows through it as there was before.

Now there can be a situation where an unusually large amount of current is forced through the wire. In that case the electrons colliding with the atoms in the wire create heat and increase the wire’s temperature. If sufficient current is forced through the wire, the temperature can get high enough to melt the wire. At these high temperatures some material could evaporate or oxidize from the surface. Such is the case with the filament of a light bulb, a tiny tungsten wire which glows at high currents. Thus, the filament evaporates and the dark residue can often be seen on the top of the bulb.

However, this type of phenomenon only occurs at high current flows, which produce high wire temperatures. Under what we would call normal conditions there is no loss of material when electricity flows through a wire.