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In this investigation I will be looking at how certain factors affect the resistance of a piece of wire.

Extracts from this document...

Introduction

The Resistance of a wire

Physics coursework

Aim

In this investigation I will be looking at how certain factors affect the resistance of a piece of wire.

Planning

All materials, solid, liquid or gases are made up of atoms. The atoms themselves consist of a nucleus that is made up of particles called protons and neutrons. Around the nucleus are electrons that have a negative electrical charge. It's the electrons on the outer shell that are the most important when thinking about conduction.

In metals, the outer electrons are held only very weakly to the atom and often drift away from the atom and go to other atoms. These wandering electrons are called conduction electrons and the more of these there are in an element, for a given volume of metal, the better the metal will be as a conductor of electricity. When you connect a battery to a wire, one end becomes positive and attracts the conduction electrons, which drift towards that end of the wire. But the electrons have obstacles to face because the metal’s atoms are vibrating in a fixed place because of their thermal energy and so the electrons collide with them and are slowed down. It’s these collisions that the electrons have while moving along the wire that we call resistance.

Resistance is the physical property of a conductor to resist the flow of electric current.  The size of the current is decided by the resistance of the circuit.  All electrical conductors resist the flow of electric charge to same extent, but some have a higher resistance than others.  The larger the resistance of a conductor, the harder it is for electricity to flow through it.

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Middle

Material Different materials have different resistances because the materials’ atomic structures are different so some metals have low resistances and some have high resistances. Therefore it is important to keep the material the same throughout the experiment unless a different material is used to check if the conclusion or theory works for all materials. If different materials are used throughout the investigation, it will affect the results. For example if sometimes copper is used and sometimes nichrome is used, the results where copper is used will be of a low resistance because of the material and not because of the diameter of the wire.  Also when using wire you are limited to the amount of variation you can use, as there are only so many elements you can use, with length the variation is infinite.

Diameter When the diameter of the wire is varied it becomes difficult to cover a wide range of results as the range of diameters available for us is very limited.  After a certain amount of diameters have been covered it would be hard to find a wire with a huge diameter, and especially at an affordable cost for the school.

After considering the four main factors that can be varied I have decided to vary the length of wire, and monitor how the resistance changes as the length of wire is varied.  The reasons I have chosen length of wire is because of the following:

  • By varying the type of wire this doesn’t give me a continuous variation, I am limited to only the few materials available to us.
  • By varying the temperature of the wire this is a very difficult factor to maintain, it would not be possible to take an accurate temperature of a piece of wire in a classroom.  The variable range would have to be high to even approach an accurate procedure.
  • To vary the diameter would also prove to be difficult.  This is because there is only a limited amount of different diameter wires of the same type available.  Also if we decided to double wire up this would also prove to cause hassles because We would be limited to how many times we could double it up because of the amount of students, and the amount of wire.
  • It’s very easy to do because it’s very repeatable and the conditions are easy to recreate.
  • After 1M the variations in resistance are very good for further analysis.

Prediction

I predict that from the results I gain in the final experiment I will derive that as I increase the length of the wire, the resistance will increase proportionally.  This means that as the length of the wire increases the number of free electrons in the wire also increases.  Therefore the chances of the fixed molecules in the material colliding with the free electrons are higher.  And the more successful collisions there are the higher the resistance.

Diagram:

Method

  • We will set up the apparatus as shown and then begin to conduct the experiment.
  • We will take the resistance every 10cm from 0cm to 100cm.
  • Once we have a clip attached to the wire at 0cm we will then place the other one at 0cm also.
  • Once the resistance has been taken at 0cm, we will then move the crocodile clip up the wire 10cm, and take a reading.  I will then continue to move the clip up the wire 10cm at a time and take the resistance until I reach 100cm.

We would now like to conduct a second method using the same wire.  This method will be to prove the results we will gain while conducting the first method.  The second method is as follows:

Diagram:

Method:

  • We will set up the apparatus as shown and then begin to conduct the experiment.
  • We will take the voltage & current every 10cm from 0cm to 100cm.
  • Once we have a clip attached to the wire at 0cm we will then place the other one at 0cm also.
  • Once the voltage & current has been taken at 0cm, we will then move the crocodile clip up the wire 10cm, and take a reading.  I will then continue to move the clip up the wire 10cm at a time and take the voltage & current until I reach 100cm.

Fair Test

For both methods I will keep all but one thing the same.  The one thing that will change is the distance between the two crocodile clips.  Although I am keeping all but one factor the same I still need to decide how I'm going to keep these factors the same.

  • Circuit Design: I will maintain the same amount of current the whole time, and I will ensure that the temperature does not change in the environment during the experiment.
  • Wire Diameter: I will measure the wire’s diameter every 20cm for 1M with the micrometer to ensure that the wire’s diameter remains constant.
  • I will ensure the wire is completely faultless, with no sharp bends and joins.  This will ensure that the results will be constant no matter which point a result is taken from on the wire.

Safety

With these experiments there is not much of an issue with safety.  I have outlined the 2 main safety issues:

  • Ensure the PSU works properly and all wires are insulated fully.
  • Do not secure the wire too tort because if it snaps it could whip you in your face.
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Conclusion

Certainty

Although I acquired one or two anomalies I feel that these were due to the problems described above.  But disregarding the anomalous results I still managed to prove my prediction, which was that as the length of the wire increases the resistance of the wire also increases proportionally to the length increase.  I also know that my results are accurate because my resistance readings for 1metre are very close to the published manufacturer’s data.  The recorded official resistance of Nickelchrome at 1m is 35.6Ω.  I took the readings 40.00Ω and 40.80Ω.  These results are very close, showing accuracy in my investigation.

Investigation Variation

This experiment produced good results with scientific proof of the results.  But to back up the prediction and final result further tests could be carried out to eliminate any possible room for error.

A variation I had in mind for this investigation would be to do an extension experiment investigating other factors considered in the planning of this investigation.  The next appealing factor to vary is the diameter of the wire.  The prediction for this is that as the diameter increases the resistance should become lower because of the collision theory.  As the diameter increases there becomes more space between the free electrons and fixed molecules therefore there will be fewer successful collisions meaning lower resistance.

I could have also worked out the resistivity of this investigation and compared it to the published data.  The equation for resistivity is R=pl/A.  Using this formula you can work it out.  Resistivity of s wire is proportional to its length.  The resistivity of wire lets you work out a wire’s resistance suing only is length, area and thickness.

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