This is a method for the Thermistors ISA in the AQA GCSE Additional Science and GCSE Physics courses.
Hypothesis
The higher the temperature the lower the resistance of the thermistor. This is because as the thermistor is heated more electrons gain enough energy to move into the conduction band and act like free electrons. This has the effect of reducing the resistance.
Equipment
Thermistor
Multimeter
Leads
Beaker (500ml)
Thermometer
Kettle
Ice
Method
Connect the thermistor to the multimeter. The multimeter is set to work as an ohmeter, measuring resistance directly. Set the scale to an appropriate range setting. Fill the beaker with ice and place the thermometer into it. Place the thermistor in the beaker so that it is totally submerged in the ice. Wait a couple of minutes until the thermistor has reached the same temperature as the ice. Record the temperature and resistance in a table. Gradually add small amounts of hot water from the kettle to increase the temperature, recording the temperature and resistance in the table. Repeat this process until the water in the beaker is at the same temperature as the kettle (water will have to be removed as the experiment takes place).
Variables
Independent - Temperature measured with a thermometer
Dependent - Resistance measured with a multimeter functioning as an ohmeter
Control - Resistance of connecting leads, pd of cell in multimeter. These can be kept constant by using the same leads and multimeter throughout the experiment.
Risk Assessment
The main risk in this experiment is burns and scalds from the kettle. This risk is low but it can be reduced further by standing up when performing the experiment and ensuring bags, stools etc are under the desk and not a trip hazard.
Equipment
Thermistor
Multimeter
Leads
Beaker (500ml)
Thermometer
Kettle
Ice
Method
Connect the thermistor to the multimeter. The multimeter is set to work as an ohmeter, measuring resistance directly. Set the scale to an appropriate range setting. Fill the beaker with ice and place the thermometer into it. Place the thermistor in the beaker so that it is totally submerged in the ice. Wait a couple of minutes until the thermistor has reached the same temperature as the ice. Record the temperature and resistance in a table. Gradually add small amounts of hot water from the kettle to increase the temperature, recording the temperature and resistance in the table. Repeat this process until the water in the beaker is at the same temperature as the kettle (water will have to be removed as the experiment takes place).
Variables
Independent - Temperature measured with a thermometer
Dependent - Resistance measured with a multimeter functioning as an ohmeter
Control - Resistance of connecting leads, pd of cell in multimeter. These can be kept constant by using the same leads and multimeter throughout the experiment.
Risk Assessment
The main risk in this experiment is burns and scalds from the kettle. This risk is low but it can be reduced further by standing up when performing the experiment and ensuring bags, stools etc are under the desk and not a trip hazard.