Page 9 - Curriculum Visions Dynamic Book

Why metals conduct electricity
Metals conduct electricity because many of the electrons in a metal are not held tightly to their atoms but are free to move around. When a source of electric current is applied to a metal (such as when a wire is connected to both ends of a battery), the electrons are attracted to
the positive end of the battery and so make an electric current flow.
For electricity to flow, the electrons inside
the metal have to be able to move easily among the atoms. Metals do not all conduct electricity equally well. Copper, silver, gold, and aluminium are among the most conductive, with tungsten being an example of a metal with much lower conductivity.
The conductivity of a metal depends on the pattern of the atoms inside it. The best conductors have a pattern of atoms that is very uniform. Metals with a less uniform pattern of electrons are poorer conductors.
When a metal is warm, the atoms have more energy and vibrate strongly, making it harder for electrons to move between them. When a metal is cooled, the atoms only vibrate slightly, and so the metal conducts electricity far better. At really low temperatures (close to absolute zero, –273°C) metals conduct electricity thousands of times better than at room temperature. This is called superconductivity.
Why some metals are magnetic
When electricity is passed through a metal, it becomes magnetic. In general, the effect is slight, but it is made more noticeable when electricity is passed through a coil of wire. The coil is called an electromagnet. Even more curiously, when a block of metal is
placed inside the coil of wire, the power of the magnetism is magnified. For most metals the increase is quite modest, just a few percent. But for iron, cobalt, or nickel the magnetism increases by thousands of times.
(Above) This light bulb filament is made from the metal tungsten. It is a relatively poor conductor of heat, and so it slows down the flow of electrons and makes the wire heat up and give out light. Tungsten has a very high melting point; so although it glows white, it does not melt.
(Below) This is a naturally occurring magnetic ore called magnetite. Its magnetism is shown by the iron filings that are attracted to its surface.
9