- Each time I move the second crocodile clip I will record the number on the ammeter telling me the strength of the current. I will repeat this with the every wire; thick, medium and thin and then repeat the whole experiment another two times. I will record my results in a table and then also do an average results table.
5. I will then record my results in a table like this:
CURRENT (AMPS)
Preliminary Experiment
I carried out a preliminary experiment to see the other factors that could affect the experiment and also to see if I could improve any of the steps in the method. This showed that the wire was very weak if given more than 5 volts because the wire lets electricity flow faster and faster which then leads to the heat eventually breaking the wire. I found that if I decreased the voltage to a reading of 2 volts the wire stayed in tact enough to give a good reading and thereby giving better overall results.
Fair test
These are the things I will do in order to make my experiment a fair test:
- Keep the voltage the same throughout the experiment (2volts)
- Use the same wires when repeating the experiment
- Making sure that the battery pack is switched on and off after every reading.
Prediction
I predict that the thicker the wire the higher the current. I think this is because as you increase the thickness of the wire, you also increase the amount of resistance. The current is the flow of electrons; the current is dependent on the amount of voltage, which is applied. Voltage is the push given to the current. The current has to go through a circuit, which contains resistance so if you increase that push you also increase the flow of the current. All materials have a slight resistance to electricity. Factors affecting the resistance are: Length, Voltage & Temperature and Surface Area.
Density has a large affect on the amount of resistance. The resistance depends upon the amount of denseness e.g. a thinner wire has a smaller surface area meaning it has tightly packed atoms which in turn rebound many of the electrons and make it more difficult for current to pass through whereas the thicker wire with the larger surface area allows more current to pass through due to a bigger area, therefore being less collisions with atoms.
Also I predict that the longer the wire the bigger the resistance, therefore the smaller the current. This is because 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, therefore decreasing the current.
Obtaining Evidence
Thick wire: CURRENT (AMPS)
Analysis
The results from the graph give a clear indication of how the current compares to the wire length. There is a very strong negative correlation. This means that when the length of the wire increases, the current decreases. The results are also inversely proportional, meaning that when one doubles the other halves even though the resistance doubles, the current decreases. An example would be at a wire length of 50 cm, the resistance is 3.38 Ohms and at 100 cm it is 6.25 Ohms. This is almost exactly double the size.
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 inversely 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.
Also the graph has shown that the thicker the wire the bigger the current. This is because there are less atoms to collide with free electrons therefore more current is able to pass through, making the resistance increase. This is also shown on my graph and table of results because with the thick wire the current with a length of 10cm is 2.44 AMPS whereas with the medium wire the current also with a length of 10cm is 2.16 AMPS.
The results that I have obtained support my original prediction. This is because in the prediction I said that as the wire length increased, the resistance should increase, therefore reducing the current. I also said that the link should be inversely proportional because as the length of the wire increases the current decreases. The results have shown that this is true.
The curved line of best fit clearly show 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 inversely proportional through out.
Evaluation
I thought that the experiment went very well and the methods of obtaining were as accurate as I could have made them as there was only one anomalous result. Also my results were very precise (0.01 of an AMP). This also shows that my results were very reliable. Though I think that the experiment could have been even more accurate if I had the equipment. Things like straight wires, a more accurate meter bridge and a stopwatch to measure how long the current was on for, for each reading are all things that could have made the results even more reliable and accurate.
The graph showed that there was one anomalous result in the medium wire, which did not fit the rest of the pattern. This error could be down to the measurement of the wire or a temperature rise. Measuring the length of the wire is an inaccuracy because the rulers used on the meter bridges are not exact, and it is difficult to get an accurate reading of length by eye, as the wire might not be completely straight or it may be of different thickness throughout the length.
My results would be difficult to improve on as they were very accurate, and there was only one anomalous results. But if I were to do the experiment again I would use a more accurate method of measurement and take a much wider range of readings and more readings so that a more accurate average can be taken.
I would also investigate other factors, such as temperature, thickness, and material to see how these effect current. I would also do the experiment under different conditions such as temperature and pressure to see if they make any difference to the current and resistance.
