The variation with temperature of the resistance of a thermistor is shown in the graph below.
A student includes the thermistor and an ideal operational amplifier (op-amp) in the circuit shown in the figure below.
Calculate the potential 
at the non-inverting input of the op-amp.
At 
, the resistance of the thermistor is 
. State and explain whether the light-emitting diode (LED) is emitting light.
Explain why the student’s circuit will not indicate any change in temperature above 
.
The resistor of resistance 
is changed to a resistor of resistance 
so that the LED switches on or off at a temperature of 
. Determine in 
.
.
is 
, so 
, this implies that the output voltage is negative. Therefore, the light-emitting diode (LED) is not emitting light.
. Therefore, 
.
