The power unit is heavy, and should be positioned carefully. Care must be taken when carrying or moving it. o Crocodile clips can pinch hard, so must not be clipped to fingers. Analysis of pilot experiment: I carried out a pilot experiment to determine which wire I should use. I tested several different wire thicknesses, and after considering a number of factors decided the best was Nickel-Chromium of 34 gauge. This was chosen because it was able to handle a range of voltages safely (other wires immediately became dangerously hot), and gave accurate, repetitive results (I tested it several times, and each time the results were the same).
As a result of potentially dangerous incidents with lesser wires, I added the safety point concerning time: the longer any wire is left with current running through it, the hotter it gets. Measurements I am going to test the chosen wire at voltages between 2 and 9 volts, the safe maximum for my chosen gauge. This should give a range of results to compare. The lengths I believe will provide the most easily comparable results are 20,40 and 80 cm, 25, 50 and 100 cm, and 30 and 60cm. You will notice that the series are multiples of one another: this allows me to test my hypothesis (of direct proportionality) several times.
I have decided not to carry out replicates because there are not enough variables to warrant them. If I follow my plan correctly, human error is unlikely and should be obvious, giving a chance to repeat the reading. Carrying out the experiment: Method: I followed the plan I originally decided upon, including the modifications I made as a result of the pilot experiment. I used the chosen NiChrome 34gauge wire, at the voltages and measurements discussed above. Results: Here is a chart showing the data I collected. It will allow me to calculate the resistance (using Ohm’s law) later. Length of wire (in centimetres)
Voltages tested (V)these lengths the wire heated quickly, and for safety reasons I stopped. Units is Amps (I) Using the above data, I was able to calculate the resistance encountered on the wire.This was done using the formula: resistance = current/voltage Length of wire 2 Units is Ohms, the standard measure for resistance Summary Length of wire (cm).
Average resistance, across voltages (? ) Standardised Table Results (for evaluation purposes)(?For comparative purposes, I have plotted my results on a graph, firstly current vs. voltage and then power vs. resistance. This will allow me to draw a successful conclusion. Conclusion From the graph I plotted, it is evident that the resistance of a wire IS directly proportional to the length, shown by the way a line of best fit passes through the origin.
This result agrees with my hypothesis, proving my prediction correct. As I discovered in my background research, resistance is a result of charged electrons, while attempting to flow through the wire, colliding with the ions that make up the wire. When they collide, they lose their energy – affecting the end voltage. My initial belief was that each length of wire had the same number of fixed ions in it – and therefore the same resistance. As you increased the length of the wire, the number of fixed ions would increase as well, by a fixed amount.
This directly proportional increase in number of fixed ions would lead to a directly proportional increase in resistance. From the results I have gathered, it seems my prediction of how electrons move is correct. Comparing my results to official industry figures (from a “standardised table of results”), I can see my results were very close, further testament to the accuracy with which I carried out the experiment. Evaluation Looking at my table of results, I can see all the values are very close – always less than 1 ohm out. This shows a high degree of accuracy, with no stray or anomalous results.
An interesting observation is that at the higher lengths (particularly evident at 100cm), the results are slightly less accurate (varying by a maximum of 1. 32? ) then at shorter lengths (varying by only 0. 17 ? at 20cm). This may be due to the fact that I started my experiment at 100cm, before moving along to shorter lengths, and as I progressed I become more competent at taking readings. Alternatively, this may be due to the state of the wire, a factor I didn’t take into account. However, these variances didn’t affect my results.
My final results are also very close to those from the Standardised Table of Results, but are slightly higher, indicating a marginally higher overall resistance (present across the readings). There are numerous ways in which this overhead occurred – perhaps due to equipment or method used – but my theory of a directly-proportional increase still remains correct, because all my readings have this gain. Consequently, my readings are still accurate, and my prediction correct. I had no anomalous (or “freak”) results and all my results showed strong positive correlation, as expected.
My results were very close to the official figures showing how accurately I carried out the experiment, which in turn gave me very reliable figures. Overall, the evidence I gathered was of sufficient accuracy and reliability to allow me to prove my hypothesis and draw a successful conclusion. If I wished to improve the experiment, I could attempt to improve the accuracy with which I measure the current, perhaps using more accurate equipment. I do not need to increase the number of measurements – the range I had was sufficient.