Variables / Factors:
- The length of the fuse wire – 1mm going to increase this, starting from 10mm, increasing it in the steps of 10mm up to 100mm.
- There is a variable that I need to keep the same.
The diameter of the fuse wire – 0.10mm.
The material of the fuse wire - copper
Diagram:
Method:
- I will set up the apparatus up as shown.
- I will ensure that I use the fuse wires over the range that I have described in my variables.
- I will ensure that I keep the diameter of the fuse wire the same – 0.10mm.
- Then I will test the fuse wire, by applying current through it until the fuse wire melts.
- Then I will record the time.
- Lastly I will do repeats to ensure that I have obtained accurate and reliable results.
Results:
Analysis:
The graph is a down wards curve, which consists of a negative gradient. This shows that as the length of the fuse wire is increased, the less current is required to melt the fuse wire. This is because, as the length of the fuse wire is increased, the rate of heat production increases. The heat produced by the current flowing through the fuse wire, is unable to escape quickly enough from the fuse wire. The wire gets hotter as the rate of heat production is greater than the heat loss from the fuse wire. Eventually, the wire’s temperature reaches the materials melting point, which causes the fuse wire to melt. There is less current that is required to melt the fuse wire, as the length of the fuse wire is increased. When the fuse wire is short, it looses all of its heat by conduction to the crocodile clips, therefore there is a down wards curve, which consists of a negative gradient on the graph. When the length of the fuse wire is increased, it begins to loose most of its heat by radiation and convection and less heat by conduction to the crocodile clips, therefore the down wards curve begins to level out. Eventually, the down wards curve on the graph, levels out completely, showing that the current no longer has an effect as the length of the fuse wire is increased. This is because as the length of the fuse wire is increased, the resistance increases and thus there is more heat production. However, also when the length of the fuse wire is increased, there is more surface area and thus there is more heat loss, as the fuse wire is exposed to more air and looses its heat by radiation and convection rapidly. The crocodile clips have no effect as the length of the fuse wire is increased, because as the length of the fuse wire is increased, the crocodile clips get further apart and the heat is unable to escape by conduction from the crocodile clips. They both cancel each other out and the crocodile clips have no effect. This is when radiation and convection begin to occur. The trend is conclusive, as I expected a down wards curve, which would consist of a negative gradient. This is because I had predicted that when the fuse wire is short, it would loose all of its heat by conduction to the crocodile clips, therefore there would be a down wards curve, which would consist of a negative gradient on the graph. I also expected that the down wards curve would eventually level off. This is because as the length of the fuse wire is increased, the resistance would increase and thus there would be more heat production. However, I also predicted that when the length of the fuse wire is increased, there would be more surface area and thus there would be more heat loss, as the fuse wire is exposed to more air and looses its heat by radiation and convection. They would both cancel each other out and the crocodile clips would have no effect.
Evaluation:
The experiment did give reliable results. This is because the results lie very close to the trend line on the graph. I can prove this by working out the distance between the furthest point from the trend line:
(60.0, 2.52)
0.02 × 100 = 0.8%
2.50
The distance of the furthest point from the trend line is only 0.8 inaccurate. This result proves that the experiment did give reliable results, as the results lie very close to the trend line.
The experiment also did give accurate results. This is because as I repeated the experiment, all of the results were very similar. I can prove this by working out the percentage difference of my results.
(Length: 10mm)
0.03 × 100 = 0.75%
4.00
The percentage difference of my results is 0.75. This result proves that the experiment did also give accurate results, as all of the results are similar.
However, the results consisted of some anomalies, which I have identified in my results and repeated. These anomalous results could be due to the human error when using the stop clock. My reaction rate could have been slower when these anomalous results occurred. This may have been the cause for these anomalous results. It could also be due to the fact that the stopwatch is not accurate enough. However, I conducted my experiment on different days, hence I was unable to ensure that the surrounding room temperature was constant in all experiments. This may have had a slight effect on the amount of current required to melt the fuse wire and inevitably the accuracy of the results. This most likely could have caused my anomalous results.
I can improve the experiment by avoiding anomalies. Anomalies can be avoided by using a more accurate stopwatch (measuring to microseconds) and by being more aware and careful when using the stopwatch. I can also use alternative clips rather than crocodile clips, to ensure that heat loss only occurs through the wire. I can use aluminium clips, which are made of a better conducting material than the material of crocodile clips. The advantage of using a better conducting material is that it consists of more free moving electrons, which are able to transfer thermal energy more quickly throughout the piece of metal. Therefore I will obtain more accurate and reliable results.
Overall, I believe that this experiment was suitable for this task, as it supported the scientific knowledge and my prediction. Therefore I was able to obtain reliable and accurate results.
In the future I will ensure that any anomalies are rectified or omitted by repeating the anomalies under the same conditions and then calculating the averages.