A-level Physics (Advancing Physics)/Metals/Worked Solutions

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1. Would you expect a metal to have more or less conductivity than a semiconductor? Why?

A metal has more conductivity than a semiconductor because a metal has more ions than a semiconductor, and hence more free (delocalized) electrons.

2. How can the stress-strain graph for a metal be explained in terms of ions in a sea of electrons?

In the elastic region, the ions are held together by the charge between them and the electrons, and they can move apart when under stress. Then, once the ions are too far apart, the bonds aren't strong enough to pull them back together, so the metal entends under the stress. Eventually, the bonds cannot maintain the structural integrity of the metal any more, so the metal 'necks' in one place, and then the metal fractures.

3. As a metal heats up, what happens to its conductivity? Why?

As a metal heats up, both ions and electrons vibrate more. This means that the collision rate between ions and electrons goes up, so it is harder for electrons to travel through the metal. So, as a metal heats up, its conductivity goes down.