In an experiment to investigate the variation of the resistance $R$ of a thermistor with its temperature $\theta$, a student measured its resistance at different temperatures. The table shows the measurements recorded. | $\theta/^{\circ}C$ | 20 | 30 | 40 | 50 | 60 | 70 | 80 | | -------------------- | -- | -- | -- | -- | -- | -- | -- | | $R/\Omega$ | 2000 | 1300 | 800 | 400 | 200 | 90 | 40 | 1. Draw a labelled diagram of the apparatus used. 2. How was the resistance measured? 3. Describe how the temperature was varied. 4. Using the recorded data, plot a graph to show the variation of the resistance of a thermistor with its temperature. 5. Use your graph to estimate the average variation of resistance per kelvin in the range 45$^{\circ}C$ – 55$^{\circ}C$. 6. In this investigation, why is the thermistor usually immersed in oil rather than in water?

Leaving Cert Physics Resistance: In an experiment to investigate

In an experiment to investigate the variation of the resistance $R$ of a thermistor with its temperature $\theta$, a student measured its resistance at different temperatures - Leaving Cert Physics - Question 4 - 2010

Question 4

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In an experiment to investigate the variation of the resistance $R$ of a thermistor with its temperature $\theta$, a student measured its resistance at different tem... show full transcript

Worked Solution & Example Answer:In an experiment to investigate the variation of the resistance $R$ of a thermistor with its temperature $\theta$, a student measured its resistance at different temperatures - Leaving Cert Physics - Question 4 - 2010

Step 1

Draw a labelled diagram of the apparatus used.

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Answer

The diagram should include the following elements:

Thermistor in a liquid (depicted as a resistor symbol connected in a circuit).
Thermometer (indicating whether it's in water or oil).
Digital Multimeter (DMM) or ohmmeter connected to measure resistance.
Ensure labels are clear, indicating which component is which, particularly noting the liquid used (e.g., water or oil).

Step 2

How was the resistance measured?

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The resistance was measured by connecting the third terminal of the thermistor (Th3) to the digital multimeter. The multimeter was set to measure resistance, indicating the state or implied measurement, ensuring that connections are secure to provide accurate readings.

Step 3

Describe how the temperature was varied.

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The temperature was varied using a heat source such as a hotplate or a Bunsen burner. By heating the liquid in which the thermistor is immersed, the temperature can be controlled and adjusted to the desired values, allowing for systematic measurements at different temperature points.

Step 4

Using the recorded data, plot a graph to show the variation of the resistance of a thermistor with its temperature.

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To plot the graph:

Label the x-axis as 'Temperature ( $^{\circ}C$ )' and the y-axis as 'Resistance ( $\Omega$ )'.
Plot the six data points corresponding to the temperature and resistance values.
Connect the points with a smooth curve, ensuring a good distribution of the data points to illustrate the general trend.

Step 5

Use your graph to estimate the average variation of resistance per kelvin in the range 45$^{\circ}C$ – 55$^{\circ}C$.

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From the graph, estimate the resistance at 45 $^{\circ}C$ and 55 $^{\circ}C$ . For instance, if you find that at:

45 $^{\circ}C$ , the resistance is 60 $\Omega$
55 $^{\circ}C$ , the resistance is 32 $\Omega$

Then, the calculation for average change in resistance per kelvin can be performed as follows:

$\text{Average change in resistance per Kelvin} = \frac{R(45^{\circ}C) - R(55^{\circ}C)}{T(45^{\circ}C) - T(55^{\circ}C)} = \frac{60 - 32}{55 - 45} = \frac{28}{10} = 2.8 \Omega/K$

Step 6

In this investigation, why is the thermistor usually immersed in oil rather than in water?

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Answer

The thermistor is usually immersed in oil rather than water because oil is a better conductor of heat compared to water. Furthermore, oil does not conduct electricity like water does, providing better insulation for the thermistor. This helps to ensure accurate temperature readings and reduces the risk of electrical short circuits.

In an experiment to investigate the variation of the resistance $R$ of a thermistor with its temperature $\theta$, a student measured its resistance at different temperatures - Leaving Cert Physics - Question 4 - 2010

Worked Solution & Example Answer:In an experiment to investigate the variation of the resistance $R$ of a thermistor with its temperature $\theta$, a student measured its resistance at different temperatures - Leaving Cert Physics - Question 4 - 2010

Draw a labelled diagram of the apparatus used.

How was the resistance measured?

Describe how the temperature was varied.

Using the recorded data, plot a graph to show the variation of the resistance of a thermistor with its temperature.

Use your graph to estimate the average variation of resistance per kelvin in the range 45$^{\circ}C$ – 55$^{\circ}C$.

In this investigation, why is the thermistor usually immersed in oil rather than in water?

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