An engineering student investigates the electrical current through a negative temperature coefficient (NTC) thermistor at different temperatures. The experimental setup consists of a DC voltage source, the thermistor, an ammeter, and a variable resistor.
Explain how a voltmeter should be connected to monitor the potential difference across the thermistor.
State why it is necessary to keep the potential difference across the thermistor constant throughout the investigation.
Explain the purpose of including the variable resistor in this circuit.
The student records the current at different temperatures and plots the results on the graph below.
The student decides to use this circuit to construct a simple electronic thermometer. Since both axes on the graph have scales from 0 to 80, they calibrate the ammeter scale directly in '∘C^{\circ}\text{C}∘C' (such that a reading of 1 mA is interpreted as 1 ∘C1\text{ }^{\circ}\text{C}1 ∘C).
Give three reasons why this thermometer is unlikely to display the correct temperature. You should refer to both the circuit and the graph to support your answer.
