An operational amplifier (op-amp) can act as a comparator. State the purpose of a comparator.
Fig. 9.1 shows how the resistance $R$ of a thermistor changes with temperature $\theta$.
The thermistor is placed in the circuit of Fig. 9.2. The op-amp can be treated as ideal. The thermistor temperature is $10\,^{\circ}\text{C}$. Find the resistance of the variable resistor $X$ that makes the output potential $V_{\text{OUT}}$ equal to zero.
The resistance of resistor $X$ is now kept fixed at the value found in (i). Describe how the output potential $V_{\text{OUT}}$ changes as the thermistor temperature is raised from $5\,^{\circ}\text{C}$ to $20\,^{\circ}\text{C}$.
The thermistor is at $10\,^{\circ}\text{C}$. Find the resistance of variable resistor $X$ needed for $V_{\text{OUT}}$ to be zero.
The resistance of resistor $X$ is now kept constant at the value calculated in (i). Describe how the output potential $V_{\text{OUT}}$ changes as the thermistor temperature goes from $5\,^{\circ}\text{C}$ to $20\,^{\circ}\text{C}$.