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

Extracts from this document...

Introduction

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

Middle

We can now use a formula to find the resistance for each minor test. The formula is:

Potential Difference ÷ Current = Resistance or R=V÷I

 Temperature V1 V2 V3 I 1 I 2 I 3 R1 R2 R3 26° 1.6 3.1 4.5 3.4 7.0 10.9 0.5 0.4 0.4 31° 1.6 3.1 4.6 4.4 9.2 13.9 0.4 0.3 0.3 36° 1.6 3.0 4.5 5.1 10.0 15.7 0.3 0.3 0.3 41° 1.5 3.1 4.7 6.0 12.3 18.4 0.3 0.3 0.3 46° 1.5 3.1 4.3 6.2 12.8 18.3 0.2 0.2 0.2 51° 1.5 3.1 4.5 7.6 15.6 23.0 0.2 0.2 0.2 56° 1.5 2.9 4.5 8.4 15.9 25.5 0.2 0.2 0.2 61° 1.5 3.1 4.5 9.3 19.0 28.3 0.2 0.2 0.2

Using the resistance results we can now calculate the average resistance for each temperature. To do this we will use this formula:

Conclusion

However, the results on the primary voltage readings graph fluctuate as the temperature rises. I did not know what to expect with these results as I had no other results to compare it with and no scientific knowledge as to how the potential difference should appear.

The average resistance for each temperature graph summarises all of the results and this shows that the resistance decreases as the temperature rises, This is what I predicted and so these results were what I expected.

Improvement

To improve this report I could have taken more readings in the same test; with more temperature readings and/ or more batteries. This would have increased the accuracy of the results but it could have been too time consuming. I could have done the same tests but repeated them with different equipment and compare the results. This would show if the equipment was faulty and if it was not it would show more results, thus increasing accuracy. Again this would be too time consuming. I found that a flaw in my report was that I did not have any scientific evidence as to how the potential difference should be. To improve my report further research is required, which will increase my understanding of what the results should be like.

PHYSICS COURSEWORK                 JULY 2003

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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