# Investigation into how the resistance of a thermistor varies with temperature.

TITLE:         INVESTIGATION INTO HOW THE RESISTANCE OF A THERMISTOR VARIES WITH TEMPERATURE

NAME:        HELEN WRIGHT

Planning

Prediction

I predict that as the temperature increases the resistance will decrease. I think this will happen because thermistors are made from a semiconductor material; at lower temperatures few electrons are able to take part in conduction. As temperatures increase more electrons are freed from atoms and are able to take part in conduction. Thus the resistance decreases.

Method

To test our prediction we will set up a circuit consisting of the following pieces of equipment:

• Wires – to connect the circuit.
• Beaker – to contain the water.
• Water – to heat the thermistor.
• Bunsen burner – to heat the water.
• Tripod – to hold the beaker up above the bunion burner.
• Gauze – to keep the beaker on the tripod.
• Voltmeter – to measure the voltage through the cells.
• Ammeter – to measure the current travelling through the circuit.
• Switch – to turn the circuit on and off to take readings.
• Three Batteries – to supply power to the circuit.
• Thermistor – to supply a resistance.

Firstly we are going to take readings from the ammeter and voltmeter when the water in the beaker is at room temperature with only one battery, then we will take the readings again at the same temperature when the circuit has two batteries and then three batteries. Next we will repeat the whole test for the following seven temperatures rising in five degree intervals. We will record all the results in a table and calculate the resistance for each individual test and then use these results to calculate an average resistance for each temperature.

Diagram

This scientific diagram shows how we set up our equipment.

Fair Testing

To ensure that this experiment will be unbiased we will use the same equipment throughout the whole test, the same volume of water and only vary two factors; the temperature and the number of batteries in the circuit. We will vary the number of batteries in the circuit because we want to increase the accuracy as testing with only one battery repeatedly will show the same result and may be faulty. Whereas, using different numbers of batteries will ...