Use band theory to explain why the resistance of an intrinsic semiconductor falls as temperature increases.
The graph in Fig. 7.1 shows how the resistance $R$ of a thermistor varies with temperature $t$. The thermistor is placed in the circuit shown in Fig. 7.2. The battery has electromotive force (e.m.f.) $9.00\,\text{V}$ and negligible internal resistance. When the thermistor is at $25\,^{\circ}\text{C}$, the potential difference between terminals A and B is $1.00\,\text{V}$. The thermistor’s temperature then changes from $25\,^{\circ}\text{C}$ to $10\,^{\circ}\text{C}$. Determine, to two significant figures, the change in potential difference between A and B.
The temperature of the thermistor in (b) changes from $25\,^{\circ}\text{C}$ to $10\,^{\circ}\text{C}$ at a constant rate. State two reasons why the potential difference between A and B does not vary at a constant rate.