(a)[2]
The op-amp circuit output potential $V_{\text{OUT}}$ reverses sign at a thermistor temperature of $4.0\,^{\circ}\text{C}$. Calculate the resistance $R$.
(b)[3]
State and explain whether $V_{\text{OUT}}$ is $+5.0\,\text{V}$ or $-5.0\,\text{V}$ when the thermistor temperature is $2.5\,^{\circ}\text{C}$.
(c)[3]
The op-amp output is to be shown with two light-emitting diodes (LEDs) labelled G and B. If the thermistor temperature is below $4.0\,^{\circ}\text{C}$, only LED G gives light. LED B gives light only when the thermistor temperature is above $4.0\,^{\circ}\text{C}$. On Fig. 7.1, draw and label the symbols for both LEDs.