A student investigates how the current in a negative temperature coefficient (NTC) thermistor changes as they vary the temperature of the water in which it is submerged.
They connect the thermistor in series with a constant DC voltage source and a digital microammeter, and place it inside a beaker of water on a hot plate. A digital thermometer is used to measure the temperature of the water.
State why the student stirs the water bath continuously before taking each temperature and current reading.
Identify the control, dependent, and independent variables in this investigation.
The student's results are shown in the table below:
| Temperature (∘C^{\circ}\text{C}∘C) | 1st reading (μA\mu\text{A}μA) | 2nd reading (μA\mu\text{A}μA) | 3rd reading (μA\mu\text{A}μA) | Average (mean) (μA\mu\text{A}μA) |
|---|---|---|---|---|
| 20 | 12.1 | 11.9 | 12.3 | 12.1 |
| 30 | 19.5 | 19.8 | 19.2 | 19.5 |
| 40 | 32.4 | 31.8 | 32.1 | 32.1 |
| 50 | 54.1 | 54.9 | 54.5 | 54.5 |
| 60 | 91.2 | 34.5 | 91.8 | 72.5 |
| 70 | 152.4 | 153.1 | 151.7 | 152.4 |
| 80 | 255.6 | 254.8 | 256.4 | 255.6 |
Identify the anomalous reading in the table by stating the temperature and the current value.
Calculate the correct average (mean) current (in μA\mu\text{A}μA) for the temperature that has the anomalous reading.
Describe the relationship shown by the results between the temperature and the current.
State how the resistance of an NTC thermistor changes when its temperature increases.
The student repeats the entire experiment but increases the constant DC supply voltage. Explain how the curve of best fit on a graph of current against temperature would change.
