I predict that the wires which measure 90cm and 100cm will have the highest resistance correspondingly because there is a longer length in which the current has to flow along. As a result there will be a large number of collisions occurring between the atoms of the wire and the electrons in the current. Adding to this the electrons have to squeeze together for longer than they do in a short wire to be able to pass along the wire, resulting in more collision between electrons and other electrons because there is a long distance for the electrons to travel.
Finally I predict that the 60cm wire will have a resistance that is greater than that of the 40cm of 50cm wire, yet will have a smaller resistance than the 80cm or the 100cm wire.
Fair test
To make this a fair test I am only going to change one variable; the length of the wire. And we will not change any other factors. Also when I repeat the experiment I will always use the same equipment, just in case the different equipment proves faulty etc. By using a brand new piece of wire in the experiment I will be making it more of a fair test. I will repeat the experiment three times in order to obtain a fair average from our experiment.
Equipment
For the experiment we will use;
1 Power Pack- I chose this instead of a battery because we needed to keep the voltage the same at all times
1 Voltmeter- I chose this because we needed to accurately measure the voltage in order to obtain the resistance.
1 Ammeter- I chose this because we needed to accurately measure the amps in order to obtain the resistance.
5 Connection leads- I chose these because they were the easiest way to connect the circuit.
Crocodile clips- I chose these in order to connect the apparatus together in the circuit.
1 meter of wire- I chose this because it was the fairest way to test for resistance.
Variables
The independent variable is the resistance of the wire.
The dependant variable is the length of the wire.
The controlled variables are the potential difference, the power pack, the voltmeter, the ammeter, the piece of wire used, the temperature. The only variable I am going to change is the length of the wire. I must keep all the other variables constant. If I did not then just one small change could completely change the outcome.
Obtaining
In order to carry out a fair and reliable test I repeated the experiment three times and then I used the mean to calculate the resistance. I decided to use readings starting from 10cm and then work upwards at a 10cm pace. By then recording ten results I am enabling myself to make more accurate results.
I will use the best apparatus available to facilitate me to obtain reliable results. For example I am going to use a brand new piece of nickel wire.
To view my results clearly I decided to put them into a clear and easy-to-read table which includes all three experiments and also includes the mean results. The resistance was worked out by dividing the mean volts by the mean amps. This is shown at the end of my table.
Analysing Evidence and Drawing Conclusions
We found that as the wire got longer the resistance got higher. The line of best fit on the graph shows this. It shows that the line travels upwards on the graph, and travels along a positive gradient.
The gradient for the graph is 1.5.
We predicted that the larger the wire the higher the resistance. In general our results fitted our prediction; because apart from a few anomalous results the points fit near the line of best fit, in a positive correlation. This can be elaborated on by explaining the reasons why the resistance in a wire goes up as the length increases.
Evaluating
Our experiment did not as well as we had expected. As you can see from our graph some of our results were repetitive and were anomalous. This was because we did not use our voltmeter/ammeter to the correct degree of accuracy. Thus our results had to be rounded, leaving many of them the same, thus leaving us with anomalous results.
If we were to repeat our experiment again we could use a more precise voltmeter/ammeter such as a digital one, this would give us a more precise graph. But because we used a non-digital piece of apparatus we found it harder to obtain accurate results; mainly due to having rounded to two significant figures only.
Also having the first result at 1.2 amps we were not able to set the scale to 1amps. Instead we had to set the ammeter to a less accurate scale of 5amps. However our experimental results are good enough to support our prediction and conclusion as they follow the line of best fit. However to improve our experiment we could use a digital ammeter/ voltmeter in order to obtain better results.
