Resistance
Length
Method
To obtain my results I will make an electric circuit placing the wire in-between an ammeter and voltmeter. Therefore I will need to use:
- Power point
- Crocodile clips
- Variable resistor
- Ammeter
- Voltmeter
- Constantan 36(the wire I am investigating)
- Wire cutters
The circuit will be set up like this, making a full circuit and allowing me to
Measure resistance using the ammeter and voltmeter:
Setting up my circuit like this will enable me to calculate the resistance using:
R = V
I
R = resistance (ohms)
V= voltage (V)
I = current (A)
To keep this a fair test, I will have to keep the following the same:
- In this experiment we will only change one factor, the length of the wire. This should affect the resistance of the wire in the ways stated in my hypothesis.
- I must keep the surrounding room temperature the same or the particles in the wire will move faster (if the temperature is increased) and this will therefore have an effect on the resistance.
- I must keep the Cross Sectional Diameter of the wire because there are more atoms for the electrons to bump into, as the wire gets thicker. This will cause a varying resistance, as the wire increases in thickness, the resistance increases. Therefore, if this were not kept the same this would not have been a fair test.
- The material of the wire must also be kept the same as different materials have different conductivity. I am using constantan 36 all through my experiment.
- The Measurement of the Variable Resistor- this is because this increases the current, and if there are more electrons flowing through this can change the resistance and temperature of the wire. This is because if there are more electrons there will be more collisions. Therefore, this must be kept the same. I will supply no more than 0.6 amps; I learnt this from my trial experiment to keep this a fair test, I will have to change the length of the wire, as this is what I am testing and this will help me obtain my results and draw a valid conclusion.
I am going to make three measurements for each length and for each current. I will then take an average and work out the resistance. I am doing this because this will make my results more accurate. My results will be precise to 0.01ohms. I will be using ten different length of wire starting at 10cm and going to 100cm. My experiment is a good way of carrying out my experiment, as it is a fair test and should produce valid results. It allows me to compare results providing an analysis and conclusion. My experiment is also a good way of carrying out the experiment because there is a larger amount of wire to travel up and therefore there will be more factors to increase resistance.
In my trial experiment I tested for how large a current I would be able to use without the smallest (least resistant) wire heating up. You are able to tell when a wire is heating up as you obtain variable results. My circuit was set up identically to the one above. My results were as follows:
VOLTAGE (V) CURRENT (A) RESISTANCE (O)
0.706 0.2 17.116
1.393 0.4 17.1583
2.096 0.6 17.05
As you can see from my results the resistance was round about the same and so temperature did not affect my results. If I had gone past 0.6A then my results would have been variable. In my main experiment my current will not exceed 0.6A and so temperature will not affect my results.
Analysis
From this experiment I have learnt that as the length of a wire increases, so does the resistance. This is because there is a larger amount of wire to travel up and therefore there will be more factors to increase resistance. In a wire there are atoms, which are built up in an arrangement that is fixed because it is a solid. Atoms increase proportionally to the amount of wire; therefore if there is more wire there will be more atoms. Atoms consist of Protons, electrons and neutrons. The protons and neutrons make the nucleus of an atom while the electrons circle the outside. Electrons in metal are freely moveable and are used as current in an electric circuit. This is because they carry a charge and can run all around the circuit with this charge. While these electrons are travelling around the circuit, atoms are sometimes in the way, causing the two to collide. This takes out some of the energy from the electron and transfers it to the atom. This is how resistance occurs. When an atom has more energy it begins to vibrate and as it receives more energy, it vibrates more. As it vibrates it is hitting other atoms around it and passes on its energy. This has a knock on effect and energises all atoms around until this energy is lost through heat. As the atoms vibrate they are more likely to hit electrons because the electrons now have less space to move through. If this is over a shorter distance there will be less atoms for the electrons to hit. If this is carried out over a larger distance there will be more atoms for the electrons to hit. This will create a greater amount of resistance. The current through a metallic conductor is directly proportional to the voltage across its ends. My results do agree with my prediction perfectly, as they have shown exactly what I described in my prediction. Firstly it showed that the resistance increased as length increased. It agreed with my heat theory, as my results were steady and not varied like they would have been if the wire became hot.
Evaluation
I believe that my experiment was a good way of carrying out my experiment as it produced precise results with enough to draw a valid conclusion. It was also a fair test because I kept the following the same: The Cross-Sectional Diameter of the wire- this is because there are once again more atoms for the electrons to bump into as the wire gets thicker. Therefore, if this were not kept the same this would not have been a fair test. The Temperature of the wire- this is because if the temperature of the wire is hotter it will cause the atoms to vibrate more, as this is energy. Therefore, if this were not kept the same this would not have been a fair test. The Material of the wire- the material of the wire is important because some materials are denser than others. This means there can be more atoms over a smaller area or the opposite. Therefore the electrons can have more/less space to get through the atoms. If this were not kept the same this would not have been a fair test. I believe my measurements were accurate enough as they were taken to 0.01§Ù, 0.01A and 0.01V. They were taken by digital ammeters and voltmeters making them more reliable. My results must also have been quite accurate as they allowed me to draw up a valid conclusion, as my results were what I expected and were largely similar. I believe my results allowed me to cover a wide enough range because I took results from ten lengths and this gave me enough to analyse. All my results agree very well with my prediction as when I repeated measurements they were very similar and my results were proportional. My results fit directly onto a line of best fit and had no anomalous results. I think it would be very difficult to improve my experiment as I got very good results. Further experiments that are relevant to my investigation would be to test it over a wider range of lengths to see if there is a slight curve as you increase the lengths or to try the same experiment using a thermistor, a semiconductor diode connected first one way and then the other way round, and a torch bulb. From these different materials I will test how their graphs compare to mine and why they are that way.
