I plan to calculate the gradients of each line. As the length increases, the value for gradient will increase. The gradient = the resistance of the wire.
Diagram
Meterstick with
Copper wire
Equipment
I am going to use the following equipment for my Investigation:
- A piece of Copper Wire
- A Ruler Stick
- Power Pack
- Variable Resistor
- Ammeter
- Voltmeter
- Connecting Leads and Crocodile Clips
Safe Test
To make this experiment safe I will make sure my Power Pack is set to a minimum volt e.g. 2-4. By doing this I will be able to prevent the Nichrome Wire from overheating and causing any burns. I will also take care in the experiment by not touching the wire whilst taking down my results as this may result in electrocutions and ensure to turn off the Power Pack each length to make sure it doesn’t again over heat and give me inaccurate data due to it being too hot and just being one set of continuous results instead of letting it cool down after each length.
Accuracy Test
To improve accuracy in my experiment I will consider the following points:
- Cut the wire to the correct length so it will give me accurate data as it will be right at the start and end and not a couple of cm’s out or in which will show on my graphs as error points.
- Make sure the temperature of the wire is the same each time I change the length so if they are more hotter than others this may give me inaccurate data to compare with others as it won’t be the same and wont be a fair test.
Working out the Average Result
I am going to work out the averages for each length. By doing this I will need to record the results more than once for different experiments for the same length so if my results are not consistent I can do it again until they are.
To work out the average result, I will add the number of results together for each length of resistance and divide it by how many there are. In this case for 10cm, I would add 3.76+3.83+3.91+4.02+3.92+3.86+3.95+3.87+3.65+3.60+3.86+3.87+3.65+3.60 = 58.96/15 =3.93. This would then be my average result and I would do the same for all the different lengths and plot it in a table so I can use them to plot it as graphs and see if I can see a relationship trend between the resistance and length as it increases.
Method:
I will be carrying out the experiment shown in the diagram that I have drawn above. Our investigation will be set up as a circuit so our results should be right. In order for me to do this I will need to connect the Nichrome Wire to the Metre Stick at all10 lengths. The lengths I am going to use are: 10,20,30,40,50,60,70,80,90 and 100cm. As I am doing this I will need to do record my results 5 times for each to make sure my results are consistent and reliable to use. If my results are not consistent I will then need to do another table until they are. By doing it 5 times I can see how the current and voltage compare as the wire also increases and also find out if the resistance increases as well by using the formulae: Resistance (Ohms) = Current (Amps) * Voltage (Volts).
In order for me to do it 5 times I will place the Variable Resister at different positions to give me different readings for Current and Voltage each time for each length of wire.
I will keep the temperature, thickness of the wire and also the amount of volts on the Power Pack the same to make sure it is a fair test apart from the length of the wire which I will change during the experiment using the crocodile clips and connecting leads. After I have collected a good range of results I will record them in tables and plot the results as graphs.
Results
Here are my results that I took down during the experiment with my group. First we started at 10cm to see if the resistance increases as we go up the metre stick. We recorded the resistance in ohms.
10cm -1st Time
2nd Time
3rd Time
Here is my first set of results .I am going to move on to 20cm and see if the resistance will gradually increase.
20cm-1st Time
2nd Time
3rd Time
I can see that the resistance is increasing however I can also see that the Voltage is increasing and the Current is decreasing as I increase the length of wire. To back this up I am going to keep going up and see if it will continue with 30cm.
30cm – 1st Time
2nd Time
The resistance is increasing which I predicted earlier; I am going to carrying on investigating and see if it still increases with 40cm now.
40cm -1st Time
2nd Time
The resistance is still increasing which I like to see. However I can still prove this by plotting my results on a graph and seeing the steepness of the trend as the length increases. I am going to move up to 50cm and do the same.
50cm-1st Time
2nd Time
3rd Time
Ever since 10cm, the resistance has increased over time. I am going to increase the length even more and continue with the next cm length which is 60cm
60cm – 1st Time
60cm – 2nd Time
The resistance is again increasing; I am going to continue with 70cm. As 100cm is my last cm that I am going to experiment with I cant go anymore longer as this is the longest the school can provide us with (unless we use another ruler) but looking at my results already I can see that its steadily increasing.
70cm – 1st Time
70cm – 2nd Time
The resistance is increasing, I am going to move onto 80cm now and see if it still works.
80cm – 1st Time
80cm- 2nd Time
The resistance is increasing as well. I am going to move onto 90cm which I predict should increase as well looking at my results so far.
90cm – 1st Time
90cm- 2nd Time
Lastly at my last cm, 100. I can see that it has increased ever since the start. This is good as it proves that my prediction is right but I am going to investigate it even more giving more detailed information on what I found out in the experiment and what my graphs shows.
100cm-1st Time
100cm-2nd Time
To make it easier to work out, I have created another table for the average results for all the lengths. I did this again by adding all the numbers up for each length and divided it by how many there were. By using this I can plot the results on a graph and see an upward trend.
Average Results
Analysis
Looking through my graphs and tables I can see that the line has an upward trend of steepness and my resistance is increasing as I increase the length as well. This has proved that my prediction is right. E.g at 20cm the resistance was 7.983 ohms, at 50cm it was 18.498 ohms and at 100cm the resistance was 36.058 ohms. I can prove this by looking at my graphs for Current and Voltage and Average Resistances.
This is because there is an Positive correlation the line which shows a direct relationship between resistance and length because the line goes straight through zero. As I did on the graph I found out that if you double the length, you double the resistance as well, I can prove this by looking at my graph and marking out say 20cm and 40cm (which is double 20), I then worked my way up the graph until I got up the line and I doubled the result it to see if it was near enough (shown on the average resistances graph). For 20cm it was 7.93 x 2 = 14.81. To make sure my average resistance results were correct I did tabulation, a simple calculation which finds out the gradient for each length on the graph, because I couldn’t fit all my lengths on one graph I only did up to 50cm which was good enough to work on. I did this by doing the following
. E.g I chose 0.2 (ammeter) and worked my way up until it reached the line and it came to
0.78 (voltmeter), I did the same thing again but on a different point, 0.4 and 1.56. I put
This into the formulae (1.54 – 0.76)/0.4-0.2 = 0.78/0.2 = 3.9 ohms which was exactly what my average result for resistance was. I did this for all 5 lengths and I have shown my results on a separate graph
As I said in my prediction, the reason why resistance increases with length is because when electrons tries to get past the metal atoms in the wire, so as the length increase they will have to get pass more atoms in the metal wire. This shows that the atoms are slowing down so therefore makes the current reading decrease as well. This is all due to there being more collisions with the atoms so there needs to be more pressure or voltage that needs to keep them going around, so more energy is transferred into the wire so the voltage will increase. R=V/I. as well as resistance.
Evaluation
This was a very good and reliable experiment that I have investigated; this is due to having accurate data and good lines of best fit but unfortunately we did have some error points here and there. Most lied on the line of best fit but others were too far out or in, this was because the wire wasn’t measured precisely to length or the clips were not positioned on the point so the clips were either to high or low on the meter stick so the wire was too long or too short. To correct these error points, I would cut the wire to length and place them exactly on the length.
I have plotted my gradient results on a graph and I can see that as you increase the length, you also increase the gradient as well. This is because there is an uptrend on the line which shows a direct relationship between the resistances gradient and the length of the wire as it goes straight through zero, which I can show on my graph.
In the experiment, I think the wire may have been overheated which then gave us incorrect data to work with. This is all because if the metal atoms are heated, they start to vibrate which means it’s harder for the electrons to pass through the wire. To correct this I would turn the PowerPack off to let the wire cool down, lower the voltage setting or even put the wire in a trough filled with cold ice or cotton wool.
To extend my investigation even more I would consider changing:
- The thickness of the wire
- or the material of the wire to see if they also affect the resistance of the wire when you increase the length.
If I did change the material of the wire I would choose:
Reason being is because I would like investigate if Nichrome Wire is more of a good conductor compared to Copper Wire which would show a difference in results or in a faster increase of resistance. This maybe because of its metallic structure in the wire, which is based on how fast the electrons will have to pass through it.