|A thermistor is an electronic component whose resistance changes with temperature. The voltage and current of a thermistor can be measured as the temperature changes. Sensors allow you to take the many readings necessary and to plot graphs of voltage and current against time. Using sensing software, the resistance of the thermistor can be calculated and the relationship of Ln(temperature) against 1/current shown on the graph.
What you need
TH7 thermistor, smoothed power supply, heater and stirrer unit, interface, temperature, voltage and current sensors.
Connect up the circuit as shown. Connect the current sensor to the first socket on the interface, the voltage sensor to the second socket and the temperature sensor to the third socket. If the sensors are adjustable, set a 1A range on the current sensor, a 5V range on the voltage sensor and a 0-100 range on the temperature sensor. Run your sensing software. You may need to do a short test run to establish a suitable voltage for the power supply. Your system may recognise the sensors automatically, otherwise you will need to set them up yourself. Set up the sensing software so that it will record for 20 minutes. Start recording as you heat water in a beaker until it is almost boiling. Allow it to cool as you continue recording.
What does the graph tell you about the change in temperature? What does the graph tell you about the change in current? What does the graph tell you about the change in potential difference? How does the temperature affect the current and potential difference?
Use the software to calculate the resistance (V / I). Get the software to plot resistance against temperature. Use the software to calculate Ln (Temperature). Use the software to calculate 1/Current. Plot this against Ln(temperature).
Is it easier to understand the relationships here by using sensors?
Activities in this section adapted from The IT in Science book of Data logging and Control. © IT in Science and may be reproduced as needed for use within your school.