# Thermistor cooled in water and effect of temperature

1. Feb 17, 2015

### Barclay

1. The problem statement, all variables and given/known data

A student investigates how the resistance of a thermistor varies with temperature using an ohmmeter. To measure the temperature of the thermistor she immerses it in a water bath. At the start of the experiment she fills the beaker with the water at 50°C. She takes measurements of the temperature and the resistance at various temperatures as the water cools down. The student adds ice to help achieve lower temperatures and stirs the water regularly. Result measurements are shown in the table.

Q1 asks: describe the pattern shown by the graph.

Q2: The student allows the water to cool down slowly during the experiment. How does this improve the accuracy of the results?

Results:

Temperature C ..... Resistance kΩ

10.......................... 12.62
15 .......................... 8.47
20 ........................... 6.61
25.............................. 5.45
30........................... 4.25
35 ........................... 3.54
40 ............................ 2.79
45 ........................... 2.11
50 .......................... 1.12

Attempt:

Q1

[When drawn the with the x-axis as increasing temperature and the y-axis as increasing resistance the graph looks like a curve declining in gradient]

Should the answer be “The graph shows a curve where the resistance declines gently at the temperature rises”. Is there a more technical description for the curve? Is it “negative correlation”.

Q2: The student allows the water to cool down slowly during the experiment. How does this improve the accuracy of the results?

Not really sure here but I would say “If the water is cooled suddenly then the molecules of the thermistor may not catch up to the new temperature so the readings will be false. Allowing the water to cool slowly allows time for the molecues of the thermistor to be at the same temperature too.

2. Feb 17, 2015

### lightgrav

Any curve is described first by its values ... the R's are all positive.
... next by the slope: it is negative (R decreases with T)
... next by its curvature: is the slope getting steeper, or flatter, at high T?
If you recognize the curve shape, you might venture a guess at the functional form - but be explicit that it is a speculation.
(ie, does it look like a straight line? does it look like a cosine? does it look like an exponential? a quadratic?)