(a)[2]
State the role of the processing unit.
(b)[3]
A student is making a sensing unit for changes in temperature. A $4\,\text{V}$ supply, a fixed resistor with resistance $2.5\,\text{k}\Omega$ and a thermistor are available. The thermistor has a resistance of $3.0\,\text{k}\Omega$ at $6^{\circ}\text{C}$ and a resistance of $1.8\,\text{k}\Omega$ at $20^{\circ}\text{C}$. Complete the circuit diagram in Fig. 9.2 to show how the resistor and the thermistor are connected so that the output is more than $2\,\text{V}$ at $6^{\circ}\text{C}$ and less than $2\,\text{V}$ at $20^{\circ}\text{C}$. Indicate $V_{\text{out}}$ clearly.
(c)[2]
Suggest two ways in which a relay is used as part of an output device.