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Resistance of a Wire

Extracts from this document...

Introduction

GCSE Physics Coursework

Resistance of a Wire

  1. Planning

  1. The Problem

The experiment is about finding how the resistance of a piece of wire changes as you increase its length in 15 cm amounts each time.

In this piece of coursework, I have been asked to investigate the factors that affect the resistance of a nichrome wire. There are many things that affect the resistance of a nichrome wire but I am investigating how the length of the wire will affect its resistance.

  1. Outline

Firstly I will explain what resistance is and how it works. Resistance is when electrons travelling in a material collide with the atoms of the material. The collisions between the electrons and the nuclei cause the electrons to move slower, this is called resistance. So, resistance is how hard it is for the electrons move through a wire material.

The uncontrolled factors that will affect the resistance of the wire are:

  • Firstly, temperature is a factor. If the wire is heated, the atoms will move around more because there will be an increase in energy. This would cause more collisions between the nuclei and the electrons. The increase in collisions would cause the resistance to rise.

    The temperature factor would be very hard to control, because the equipment needed to keep a constant temperature has not been given to us. So we will attempt to do this by being as quick as possible when taking the readings so as to have the same temperature throughout the experiment.

image00.png

  • Secondly, the thickness of the wire is a factor. The thickness of the wire will cause resistance to decrease because of the increase in space in the wire. The increase in space means that there is more space for the electrons to flow freely because there would be fewer collisions with atoms.
  • Thirdly, the material used would be a factor. If the material being used contains atoms with a large numbers of free electrons on the outer shells, then this means there are more electrons available. So, in theory, if the material is dense the number of atoms is high so the number of free electrons is also high. However if the atoms in the wire are dense with little free electrons, then this will cause an increase in resistance, due to frequent collisions with the nuclei.
  • Finally, the length of the wire is a factor. The longer the wire, the longer it will take electrons to get to the end of the wire. This is because there will be more collisions between electrons and nuclei. So, in theory, the length of the wire should be directly proportional to the resistance. This is because electrical resistance may be thought of as an interference with the free flow of electrons. If the wire were a superconductor, there would be no obstacles to this flow and resistance would be zero, regardless of the length. But there are impediments and the longer the wire; the more of these are encountered.

One obstacle to the free flow of electrons is the lattice of the atomic nuclei that make up the metal. Another factor is impurities in the metal, which have a higher resistance than the pure metal. If you double the length of the wire you have twice as many of these obstacles to overcome.

  1. Steps to Ensure Accuracy

Things we can use to ensure the accuracy of the results of the experiment are:

  • Accurate multi-meters so that you get accurate results and not too many anomalies
  • Accurate metre rule so that you get accurate lengths of wire
  • Appropriate power source such as a power pack to get the right voltage

I plan to take 15 sets of results for each trial over a range of 15 – 75cm at 15 cm gaps. I will need to repeat the experiment three times which means I will get 30 readings. I will do this to make a fair test and to make it more accurate I will take the average of the results to get a single answer.  

With regards to scientific knowledge I already know that that Volts = Current x Resistance  (V = I x R)

I know how to measure Current and Voltage with a digital meter and how to measure length with a metre rule.

  1. Prediction

I predict that, the longer the wire is, the more resistance there will be due to the collisions between the electrons and nuclei. In theory, if the length of wire is doubled, then will the resistance will double as well. Because the number of atoms is doubled, it will cause there to be twice as many collisions. I think that I would find out that the longer length of wire the more resistance there would be because the more wire means more particles for the electrons to collide with. I think that there will be a pattern between voltage and amps (current) because as the voltage increases so does the amps. In theory the resistance in the circuit at zero length should be zero, but the connecting wires and the internal resistance of the power pack means that this is not the case.image09.png

  1. Equipment

The equipment that I will need is:

  • Nichrome wire
  • A metre ruler
  • Crocodile clips (2 of)
  • Connecting wires
  • Power pack set on 2 volts
  • Digital voltmeter
  • Digital ammeter

To calculate the resistance of the wire I used this formula: Resistance = Voltage/Current (R = V / I)

  1. Safety Precautions

The precautions that I will take are:

  • I will keep all electrical appliances away from water - this includes the length of nichrome wire.
  • I will keep the voltage at the correct voltage because if the nichrome wire becomes too hot it could burn someone; start a fire on the wood it is mounted on or the thin wire could break in the heat.
  • I will need to check that the power supply’s overload switch works in case there is too much current flowing through the wire, which would cause the wire to get hot. This increases the fire risk and the chance somebody could burn himself or herself.
  • A Carbon Dioxide Fire Extinguisher was in the lab in case of fire.
...read more.

Middle

        Meter ruler

image03.png

                   Connecting wiresimage04.png

image11.png

image05.png

Length of nichrome wire                

image06.png

Voltmeter

The following table is an example of what I used to record my results in during the experiment. The last column was used to record the resistance in ohms which I calculated after the experiment using Ohms law, (V = I x R)

Length

Volts

Amps

Ohms#1

15

30

45

60

75


  1. Results

The results

...read more.

Conclusion

Therefore there will a direct proportion between the length and the resistance if the wire increases or decreases in length, so will its resistance.

  1. Suggestions for Further Experiments

  • A further experiment that could be carried out is changing the width of the wire instead of the length of it.
  •  Another way of doing this is by using different widths of wire; for example thin, medium, or thick nichrome could be used to show how the resistance is proportional to each other to the width as it is to the length.
  • And I could use the same length and width of many different materials of wire, using the same amount of voltage each time. To show that resistance and length or width are proportional to each other in all metals
  • A further experiment that could be done is trying different widths together with different voltages. Using different types of wire would have allowed me to compare the resistance difference between wires would also make an improvement.
  1. Bibliography

The following sources of information were consulted:

Internet Links

http://www.bells3.freeserve.co.uk/cors/wire.doc

http://www.courseworkbank.co.uk/GCSE/

...read more.

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