I will be investigating how the length of wire, when changed, affects resistance. If I was to double the length of the wire, the resistance would also double. The amount of collisions that would take place would also double as the number of atoms would double.
In my circuit, I am going to connect a resistance wire. I can vary the length of the wire and record the resistance reliably. This will show me how the resistance is affected.
I am going to set up the experiment as shown.
I am going to connect the ammeter in series to the resistance to measure the current in amps. I will connect the voltmeter in parallel to the resistance wire. The 6 measurements I plan to use are 15, 30, 45, 60, 75 and 90. The formula for my calculations will be:
To make this a fair test, I am going to make sure of a number of things. I am going to use a metre rule to measure the length of the wire so the measurements are accurate. I am going to keep the same thickness and type of wire and the temperature will be the same. The voltage and adjustment will be the same as well. The only factor I am changing is the length. To make the experiment safe I will not allow the wire to get hot, and I will avoid short circuits. To make sure this happens I am going to do a trial run to help establish a suitable voltage for the power supply.
I have chosen 6 measurements, which are sufficiently different, as they will produce a good range in my resistance results. The measurements I have chosen are 15, 30, 45, 60, 75 and 90. To achieve reliable results I will repeat the results twice. To control the temperature of the wire, I will make sure I have a suitable voltage and wait for a minute or two between each result for the wire to cool down if it does get hot.
I left a 15cm gap between each measurement to make sure I will get the most reliable results that I can. This wide gap also prevents heating of the wire as if the measurements were close together only a certain part of the wire would get heated resulting in the wire increasing in temperature quickly.
Obtaining Evidence
Analysis
My graph shows the line of best fit going straight thought 0, this shows that Resistance is proportional to Length. The graph is a straight diagonal with no anomalous results. If the length of the wire is doubled, then so is the resistance, this is shown on the graph at 45cm and 3.6ohms, if the length is doubled to 90cm the resistance is also doubled to 7.2ohms. This shows that the resistance is quantative.
If the length of the wire is increased, the numbers of atoms are increased aswell. This means that there are more collisions between the electrons and atoms as there are more atoms for the electrons to collide with, resulting in the resistance increasing. So when the length of wire is increased, so is the resistance. This shows us that resistance is proportional to length.
My graph supports my prediction by going straight through 0, which tells us the Resistance is proportional to Length and proves that my prediction is right.
Evaluation
The method I used to carry out the investigation was a good one as I achieved good and reliable results. My results showed me clearly that Resistance is proportional to Length.
There were no anomalous results, this shows that my graph and results are very accurate as every result goes straight through the line of best fit and when the experiment was repeated, my results were very close or the same to each other.
The reason for my accurate results is because I kept the temperature under control. I did this by choosing an appropriate voltage so the wire would not get too hot and also leaving the wire to cool for a few seconds before I got my next result.
To extend this experiment, I could have made more measurements to see if they took the same path as the others.
Nina Ryner
