A circuit incorporating an ideal operational amplifier (op-amp) is shown in the figure below.
The variation with temperature 
of the resistance 
of the thermistor is shown in the graph below.
The output potential 
of the op-amp circuit changes sign when the temperature of the thermistor is 
. Calculate the resistance 
.
State and explain whether the output potential is 
or 
for a thermistor temperature of 
.
The output of the op-amp is to be displayed using two light-emitting diodes (LEDs) labelled G and B. When the temperature of the thermistor is below , only the LED labelled G emits light. The LED labelled B emits light only when the temperature of the thermistor is above . On the figure above, draw and label the symbols for the two LEDs.
.
. Thus, 
, and hence the output is 
