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Investigating how temperature affects the resistance in a wire

Extracts from this document...

Introduction

Investigating how temperature affects the resistance in a wire

Prediction / theory:

All substances in the world are made up of protons, neutrons and electrons. All atoms have a nucleus in the centre that is made up of neutrons and protons, and a certain number of electrons circling around it; these electrons circling around the nucleus have a negative charge. These electrons orbit the nucleus in shells; they occupy different shells with the rules that:

-The first shells (nearest to the nucleus are always occupied first

-The maximum of electrons any shell can hold is 2n^2 (where n = the shell number)

-The outer-most shell containing electrons can only hold a maximum of 8 electrons

To demonstrate this here is a model of a metal atom (iron):

All metals are known as n-type semiconductors as they all conduct electricity but all have resistance at room temperature.

Metal atoms can bond together to form a giant structure, which is held together by metallic bonds; this means that there are many free electrons in these structures. This is because the metal atoms in the metallic structure have electrons on the outer-most shell that pass freely from one atom to another; these electrons can carry heat from one metal atom to another (making metals good conductors of heat). The electrons in these metal structures can be ‘pushed’ in one direction buy a lack of electrons or a abundance of electrons in one area, as the electrons flow through the metal a current and electricity is produced. The current is therefore, the speed at which the electrons flow through a circuit and the voltage is the driving force that pushes the electrons (usually provided by a cell).

Middle

2.4

1.02

1.02

1.47

0.48

0.85

0.52

0.73

I am now going to display these results in the form of a line graph, so that any patterns or correlation can be made on the results. To give an idea of how accurate the results are and what range the true results should be, I have used error margins. When collecting results for this experiment the accuracy for getting the actual temperature at higher required temperatures decreases; this is because at higher temperature there is a greater temperature difference between the water bath and the surrounding area. This means that at higher temperatures the temperature of the water bath can drop quicker than at lower temperatures (where the temperature difference is less). To represent this opening for inaccuracy, I have used x-axis error bars on the results with an error amount of 5% of the value (temperature for that result). The x-axis error bars only go lower than the associated result value. This is used to represent the fact that at any temperature along the scale used in the experiment (with the exception of 10°C), the actual temperature could only be the temperature or lower due to the temperature drop effect. A 5% value is used in the x-axis error bars because it incorporates the notion that the inaccuracy goes up with a rise in temperature. Making the x-axis error bars bigger at higher temperatures and smaller at lower temperatures.

There is also the possibility of inaccuracy among the ohms readings, due to the possibility of inaccuracy in the multi-meters that were used to take volt and amp readings. To represent this opening for inaccuracy I have used y-axis error bars on the results with an error amount of 2.4 either side of the values.

Conclusion

°C there would be infinity resistance, since infinity can never be reached, and the conclusion did not take into account β, that conclusion was wrong.

My second experiment and therefore the investigation failed to take this into account. However since I was using much lower temperature to investigate the relationship, there is no way I could have known about it. Or for that reason, β is so small I would probably not have been able to detect β using the apparatus I used in my experiments. However, at these very high temperatures where β starts to have an effect, most metals are near to their melting points, so this knowledge concerning β is therefore not very useful because it make very little difference before the metal melts and it’s electrical properties change (it becomes an electrolyte).

Therefore I can conclude that this investigation went well, enabling me to make accurate conclusions about the relationship between the resistance and the temperature. It primarily told me that the resistance = a (or k) * the temperature, since the title did not specify which metal or substance the relationship would have to be based on.

If I were to do this experiment again, I would make sure it is isolated as much as possible from any factors, which could affect the experiment out of proportion. I would therefore change the method and apparatus as appropriate to make sure these factors would not affect the results. To ensure more accurate results I would use apparatus that measures the resistance to a greater degree or accuracy. My first investigation was not a fair test, but my second was a fair test because the factors, which could have affected the results, were isolated from the experiment.

I don’t think I needed to do any extra research on the subject because I clearly had easily enough to back my results up and to show why certain results were anomalous.

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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