∙ The conductivity of the metal, the reason for this is because if a metal is a poor conductor it will not allow electrons to pass through easily e.g. Nichrome, but if I have a good conductor e.g. copper it would more than likely allow electrons to pass through it easier.
How I will make sure that temperature doesn’t affect my readings or results.
To avoid the heating up of my wire I will take my results as quickly as possible as the collisions within the wire creates heat and therefore raises the temperature of the wire, this in effect could change the reliability of it.
Equipment I will be using.
∙ Power pack
∙ Ammeter
∙ Voltmeter
∙ Variable resistor (rheostat)
∙ The wire (28 Nichrome)
∙ Crocodile clips
Set Up The Apparatus As Shown:
+
Key: Power Pack
A Ammeter
+ Wire V Voltmeter
A
R
Rheostat
+ V
Plan.
To discover how length affects resistance I will be using 28 Nichrome at the following lengths: -
- 10cm
- 20cm
- 40cm
- 60cm
- 80cm
- 100cm
With each piece of wire I will place it into the resistor mount, then using the rheostat I will adjust the current until it reads 1 volt on the voltmeter. When this is done I will note down the reading on the ammeter, then I will go up to 2 volts, followed by 3 volts then finally 4 volts. This method will be repeated for each length of wire and with the results I will work out the resistance with Ohms law V= I * R.
S I will be using the same type of wire and the same equipment throughout.
A The length of the wire and the voltage (Current)
M The voltage, amps and the wire length.
Prediction.
My prediction is that as you increase the length of the wire the resistance will increase, as the flow of electrons will be resisted more as there are more particles within the wire to resist the flow, therefore more voltage will be required to push the current through.
(Rough Estimate)
Ω V A V A V A V A
10 0.71 1 1.4 2 2.8 3 4.2 4 5.6
20 1.42 1 0.7 2 1.4 3 2.1 4 2.8
40 3.5 1 0.4 2 0.8 3 1.2 4 1.6
60 5 1 0.2 2 0.4 3 0.6 4 0.8
80 6.66 1 0.15 2 0.3 3 0.45 4 0.6
100 10 1 0.1 2 0.2 3 0.3 4 0.4
My theory behind the prediction is that as you increase the length of the wire, you also increase the resistance, as described above and in my theory, as you double the voltage, the reading on the ammeter should also be doubled or near enough for example 1 volt = 0.9 on the ammeter 2 volts = 1.8 etc.
Also as the length of the wire is increased for example if it was doubled the resistance would be twice as much e.g. 10cm of wire has resistance of 0.71 and 20cm of wire has resistance of 1.42.
Safety.
That all the electrical equipment I will be using will have been tested for safety and that my plan for finding resistance is approved by the teacher.
Preliminary Experiment.
V A V A Ω
10cm. 1 1.27 4 4.8 0.8085
Ω 0.787 0.83
100cm. 1 0.12 4 0.46 8.51
Ω 8.33 8.69
Conclusion my Preliminary Experiment.
For the preliminary experiment I did the shortest wire with the lowest and highest voltage, and the longest wire with the highest and lowest voltage, and from this I have found my plan to be satisfactory and that the results are fairly even so my method and plan will remain the same as before.
Results.
V A V A V A V A Ω Average.
10cm 1 1.24 2 2.42 3 3.8 4 4.7 0.8125
Ω 0.8 0.82 0.78 0.85
20cm 1 0.55 2 1.05 3 1.55 4 2.05 1.8975
Ω 1.81 1.9 1.93 1.95
40cm 1 0.27 2 0.54 3 0.81 4 1.18 3.7
Ω 3.7 3.7 3.7 3.7
60cm 1 0.15 2 0.3 3 0.45 4 0.6 6.66°
Ω 6.66° 6.66° 6.66° 6.66°
80cm 1 0.13 2 0.26 3 0.39 4 0.52 7.69
Ω 7.69 7.69 7.69 7.69
100cm 1 0.1 2 0.2 3 0.31 4 0.41 9.86
Ω 10 10 9.68 9.76
Graphs!
Problems that I could have encountered.
Because this experiment was spread over one lesson, I ended up having to use different equipment (e.g. Ammeters etc.) this may have modified my results slightly as no 2 pieces of electrical equipment are usually ever the same. Also due to mains power always changing in current value this may also have modified results.
Conclusion.
I came to the conclusion that as wire length is increased, the resistance is also increased this is because as the wire length gets longer, there will be more particles within the wire which can cause resistance, i.e. charged electrons within the current will have a higher collision rate than they would in a short wire therefore more resistance is given. So as wire length increases more voltage will be required to push a current through, the shorter the wire the lower the voltage that is required. (Refer to: What is resistance and how can it affect electricity? For wire length theory)
The final results I find to this experiment are to my liking as the results follow a similar pattern to that of my prediction i.e. 1 volt = 0.9 on the ammeter 2 volts = 1.8 etc. this to me means a success as the experiment has done what I thought it would do.
Evaluation.
I found that the method that I used was suitable to the experiment and the experiment proceeded without a fault and the evidence which I obtained of discovering how wire length effects resistance was very conclusive for as the results show, resistance does increase as wire length is increased. The results obtained also show that the experiment was reasonably accurate as the results obtained varied only marginally (at a difference of 0.4 either side at the most), which shows that the method was also good enough for the purposes of this experiment.
If I were to do this experiment again though, I would choose a much wider variety of wire lengths and wire types, and repeat each voltage for each wire length at least 3 times to get an accurate average for each wire length, for I find that these few results do not offer enough variety to provide sufficient evidence to support my theory (title), following that I would also like use the same equipment throughout the experiment to avoid any possible differences within the equipment.
