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

1. What is the resistivity of silicon, at room temperature?

$\rho =\frac{1}{\sigma }=\frac{1}{435\times 10^{-6}}\approx 2300\mathrm{\Omega }\text{m}=2.3\text{k}\mathrm{\Omega }\text{m}$

2. What sort of variable resistor would a semiconductor be useful in?

A thermistor, as the resistance of a semiconductor decreases as heat increases (but, assuming use of a potential divider, the voltmeter would have to be on the other resistor).

3. If positive ions are added to silicon (doping it), how does its conductivity change?

Positive ions mean more free electrons, and so greater conductivity.