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Resistance of a wire.

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Introduction

Resistance of a wire

Electricity is conducted through a conductor, in this case wire, by means of free electrons. The number of free electrons depends on the material and more free electrons means a better conductor, i.e. it has less resistance. For example gold has more free electrons than iron and as a result it is a better conductor.

The free electrons are given energy and as a result move and collide with other free electrons that are next to it. This happens across the length of a wire and the electricity is conducted. Resistance is the result of energy lost as heat. It involves collisions between free electrons and the fixed particles of the metal, other free electrons are impurities. These collisions convert some of the energy that the free electrons are carrying into heat.

The resistance of a length of wire is calculated by measuring the current present in the circuit [series] and the voltage across the wire [in parallel]. These measurements are then applied to this formula.

V / I = R

[Where V= Voltage, I= Current, and R= Resistance].

Ohm’s Law:

Ohm’s Law states that the current through a metallic conductor (e.g. wire) at a constant temperature is proportional to the potential difference (voltage). Therefore V / I is constant.

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Middle

I only done this experiment once therefore did not have a selection of results to investigate; I will therefore have to make all my judgements on the set that I do have.

Aim of Main Investigation:

My aim is to investigate if the thickness of a wire affects its resistance.

Apparatus:

I will be using the same pieces of equipment that I used in my preliminary investigation, but this time I will have a change in the wires, I will have four wires of the same material but of different diameters.

  • Power supply
  • Voltmeter
  • Ammeter
  • Crocodile clips & connecting wires
  • 4 Coiled resistance wires of different diameters.  [Nichrome].

Prediction:

My hypothesis is that the thinner the wire, the lower the resistance. The thicker the wire, the higher the resistance.

An atom consists of a nucleus and orbiting electrons. These electrons can create a flow of current, so the more free electrons here are, the more conducting capability that material has.

Wires with wider diameter have more free electrons because the cross sectional are is proportional to the length, so the wider the wires are the less reactive they will be and the more resistance they will have. Resistance is proportional to the cross section area of the wire given that the length and the material are the same.

Method:

  • Firstly I picked out 4 different types of diameters for my wire.
  • I chose to use 26, 30, 32, and 34. I chose thickness’ that were quite close together.
  • I set up my diagram again in the same position shown in diagram 1.
  • I attached the crocodile clips to the coiled wire that had a gauge of 26.
  • I turned the power pack on and let a current of 0.1 amps flow through.
  • I read the reading on my ammeter and voltmeter and recorded it.
  • Once I had done this I changed the wires until I had repeated the experiment 4 times one for each diameter.
  • Lastly I drew graphs as a clearer way to interpret my results.

Plan:

I predicted that the thinner the wire the lower the resistance and the thicker the wire the higher the resistance.

This is because the thinner the wire is the less paths there are for the electrons in the wire therefore it is easier it is for the current to flow. This results in the energy not being able to spread out as much, so the resistance will be higher.

If the diameter of the wire is thicker more electrons can go through the wire, therefor less resistance. The atoms from the metals cannot stop or collide with as many electrons because the diameter of the wire is larger.

I will use a rheostat, as a power supply this once turned on will allow the current to flow in my circuit. I will use crocodile clips and connecting wires to connect the components in my circuit. An ammeter to record the current. A voltmeter to record the voltage (potential difference). I used nichrome wires of different lengths and thickness’ to carry out my investigations.

Variables:

The investigation is to investigate the resistance when the diameter has changed. In order for the investigation to be a fair test all other factors should be kept constant, this has to be done otherwise the results would be inaccurate and the conclusion would also be affected. The variables, which we must keep constant, are:

  1. Temperature:

When the temperature of a metal increases so does its resistance. This is because when the temperature increases the atoms of the metal vibrate more vigorously 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 increases the amount of resistance. However it is hard to keep the temperature at room temperature especially as it may 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. The temperature cannot be investigated because it is hard to control the range of temperature needed without the correct apparatus,

  1. Length of wire:

The larger the length of the wire, the larger the resistance this is because there are more atoms from the metal so there is more chance that the electrons would collide with one of the atoms therefore there is more resistance. It is important to keep the length of the wire the same each time otherwise it could not be certain which variable is changing the resistance. Electrons have a longer distance to travel so there are more collisions. The length of the wire will make a difference to the resistance. This is because when you have a long wire the electrons have to squeeze together for longer to be able to pass through

A short wire.

  1. Type of material:

Different materials have different resistance’s because the materials atomic structures are different so some metals have low resistance’s and some have high resistance’s. 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 use throughout the investigation it will affect the results. The type of material will affect the amount of free electrons that are able to flow through the wire.

The amount of free electrons depends on the amount of electrons in the outer shell of the atoms, so if there are more or larger atoms then they must be more electrons available. If the material has a higher number of atoms there will be a higher number of electrons causing a lower resistance because if the increase of the number of electrons. If the particles in the material are tightly packed together, the electrons will have more collisions and therefore more resistance.

All these factors must be kept constant to make the investigation fair. The same apparatus must be used throughout the investigation. It is also important to take three repeats. So if one result is inaccurate the others will cancel it out.

Safety:

  • Make sure that the circuit is properly connected before turning the power supply on, and do not touch the apparatus until it is switched off.
  • The changing of the wires should only occur when the power is off.
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Conclusion

Evaluation:

I am pleased with the outcome of my experiments and am happy with the results I was left with. I feel that my results are very reliable, the reason I think this is because the results of my experiments were very similar and underwent the same pattern. If they had not been and the results differed largely from one another, then I would have believed that something had gone wrong and tried to work around it.

All my experiments showed that as the resistance increased so did the thickness, and as the thickness decreased so did the resistance. Because all my results turned out like this I came to the conclusion that yes my results were very reliable.

My working method was a good one, if I had time I would have chosen a variety of metals and kept a constant time and may have even tried more thickness’ this time very close together.

Quite a lot of repetition occurred this helped the results to be very close together.

I do believe that my method was a sensible way of testing out my prediction everything was done separately giving me a chance to focus. I cannot be certain but I am pretty sure that my evidence supports my conclusion.

Farah Ahmed

11J

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