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resistance of a wire

Extracts from this document...

Introduction

c/w

Exam No:Exp No:Centre No: 52413

Planning

I am going to investigate how the resistance varies with the length of a piece of wire. The resistance of a wire depends on certain factors. Some of these variables are listed below:

  • Length of wire
  • Diameter of wire
  • Temperature at which wire is at
  • The material of which wire is made out of
  • The potential difference across circuit
  • Cross sectional area

These must be kept constant (except the length of the wire). The three major factors are explained bellow:

Temperature:

When the temperature of a metal increases the resistance of that metal increases. This is because when the temperature increases the atoms of the metal vibrate more vigoursly because of the increase in energy. This means that the electrons have more difficulty getting through the wire as they collide with the atoms which are in their pathway.  This increases the amount of collisions therefore there is more resistance. However it is hard to keep the temperature exactly the same as the room temperature might change from day to day. It is essential to use a low voltage because it means a low current that will not heat up the wires. If a high voltage is used the energy would be in form of heat which would make the experiment unfair. The investigation will be done at room temperature.

Length of wire:

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Middle


Wire Constantan, to use to test the resistance in the circuit and conduct electricity.
Meter Rule,
to accurately measure the length of the wire constantan.              
Crocodile Clips,
to provide safe contact between the components and the wire
Wire clippers,
 to safely cut the wire when reducing it’s length.                             Wire-board, to safely and accurately hold the wire.

image11.png

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I set the equipment up in the above way. I measured the length of the wire from one crocodile clip to the other showing the distance the power is passing and to measure the voltage, current and resistance we used the power pack as well at 2 volts.

Safety

Handle the power supply carefully.
Be careful when touching the wire, as it may be hot.
Start on the lowest current, so the wire then will not melt or burn instantly.
Be careful when the wire is connected, as it will get hot.
Be careful when cutting the wire.
Make sure the main to the power supply is switched off when removing the wire from the circuit to be measured.                                                                              Keep my work area clean and tidy to avoid confusion.

Predictions:

I think the longer the wire transporting current the higher shall be the resistance because the longer the wire the longer it takes the electrons to go through and also find it difficult as more collisions occur during the flow.

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Conclusion

The results from the graph give a clear indication of how the resistance compares to the wire length. There is a very strong positive correlation.

The theory behind this is explained in the prediction. In any given metal wire, there are a number of atoms and free moving electrons. Electricity is the movement of these electrons through the wire. Resistance is caused when the free electrons moving through the wire collide with the atoms making their path through the wire more difficult. This means that if there are more atoms in the way to collide with the free electrons the resistance is increased. In a length of wire there will be a number of atoms, and in a wire twice the length, there will be twice the number of atoms. In turn this will lead to there being double the number of collisions between the electrons and the atoms increasing the resistance by 2. This explains why the results were directly proportional. For example a wire that was 10 cm long may have 500 atoms blocking the electrons. Therefore in a wire 20 cm long, there would be 1000 atoms meaning that the resistance had doubled.The line of best fit clearly shows that the results followed the expected pattern very well. The points are very close if not touching the line. This shows how the results were directly proportional through out, as the gradient remained the same.

Below you can see a small picture of my theory:

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This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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