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Investigating Resistance in Wires

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Introduction

Investigating Resistance in Wires

Plan

Aim

Our aim was to investigate the resistance of a piece of wire, and to try and find the relationship between the length of a section of wire and it’s resistance. To do this, we are planning to use a one-metre length of wire and measure off the different sections. We will take values for the amperage and voltage of each length, repeating each experiment twice to ensure accuracy. The major problem we are likely to come across is the wire heating up, as this will cause inaccuracy in the readings.

        The equipment will be set up as below,

Measurements

We decided to take values of voltage and amperage, then use Ohm’s Law to find the resistance value. We will take readings at 10cm intervals between 30cm and 100cm, giving us a total of eight values. We chose to start at 30cm rather than 10cm as starting at 10cm would be too short a distance for the electricity to travel through causing over-heating of the wire leading to inaccuracy of results.

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Middle

                   5.20

                   0.17

                 30.59

                 90.00

                   5.06

                   0.14

                 36.14

               100.00

                   5.13

                   0.12

                 42.75

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The first time we did the investigation, we got a very unreliable set of results, after investigating the cause, we deducted we had a faulty battery pack, so decided to re-do investigation, this time our results were a lot more reliable, but to ensure accuracy, we repeated each length twice

Length

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Conclusion

  • We assume the cross-section of the wire is constant throughout the length, i.e. a constant diameter.

    1mm diameter                                    0.950mm diameter

 1 x 3.142 = 3.142 mm²                        0.950 x 3.142 = 2.985 mm²

This change in diameter will cause a funnel effect, restricting the progress of the free electrons between the atoms, This would provide inaccurate results, leading to a false impression. If this fault occurs at the start of the wire it will affect all the results, if it occurs towards the end, it would change the pattern of results, causing incorrect placement of the line of best fit.

Improving the accuracy

The accuracy of this test can be improved in many ways:

  • The use of a Jockey (thin blade contact) to increase accuracy when measuring the sections of wire, guaranteeing accurate lengths.
  • Higher specification (more accurate) Ammeter and voltmeter.
  • Increase increment value i.e. 100cm. steps instead of 10cm, broadening  the range of results leading to a more accurate graph.
  • Add one large distance to confirm analysis of linear relationship (see analysis for extrapolated result)
  • The use of a constant power supply as the batteries will drain during the test, falsifying the results.
  • Ensure wire is of a constant cross-section (see above).

...read more.

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