Method (Continued ) 8. Repeat steps 6 and 7 every 10 °C for another 5–6 readings. (Do not go over 100 °C.)
9. Record all of your results in the table and plot a graph of resistance versus temperature. Resistance (R)(Ω) Temperature (θ)(˚C)
Characteristic graph R (Ω)
(°C) M5.5b
Result
• Resistance readings vary as temperature changes. • The higher the temperature, the lower the resistance achieved.
Conclusion
A semiconductor thermistor conducts better as it heats up. This can be seen from the plotted graph. The resistance falls sharply as the temperature increases.
Errors
The following errors should be considered when conducting this experiment:
• difficulty in determining the correct resistance reading at the same time as the temperature reading
• unequal thermal variations in the glycerol and/or the water
• increased resistance in the connecting wires from thermistor to ohmmeter.
Precautions
• Make sure to work with your lab partners in taking measurements. As long as both readings are taken simultaneously, they will correspond correctly.
• By heating the water very gradually, there will be fewer ‘hot spots’ created in the glycerol. Remember, the glycerol is used because it limits the convection currents and allows a good thermal connection to the devices.
• Check the resistance of the wires before starting the experiment and factor this in to your final answers.
Possible exam questions
1. Why is glycerol used in the test-tube? 2.
3. Why is the water heated gradually?
Why are the thermistor and thermometer not placed directly in the beaker?
