An operational amplifier (op-amp) may be used as a comparator. State the function of a comparator.
The variation with temperature 
of the resistance 
of a thermistor is shown in the graph below.
The thermistor is connected into the circuit shown in the figure below.
The op-amp may be considered to be ideal.
The temperature of the thermistor is 
. Determine the resistance of the variable resistor X such that the output potential 
is zero.
The resistance of the resistor X is now held constant at the value calculated in (i). Describe the change in the output potential as the temperature of the thermistor is changed from 
to 
.
.
, therefore, the output potential 
). At the temperature 
, therefore, the output potential 
). So, the output potential 
