Resistance of a wire. Jack has been given a second hand D.C. dynamo and lamp. He wants to attach these to his bicycle and produce most light without blowing the bulb. What wire should he use?

As you can see there is a correlation between the SWG and the resistance, this is that the lower the SWG the lower the resistance. We now decided to back this up with results from a Multimeter.

Testing SWG using Multimeter …..









As you can see, the results aren’t exactly the same but they still show the correlation that the lower the SWG the lower the resistance. This is because I lower SWG has a smaller diameter; this allows more electrons to flow through the wire.

After this we decided to choose the SWG 18 constantan as the type and diameter of wire we used. This is because it has the least resistance yet it is the thickest, therefore it will not get to hot too easily.                        

Now we decide to test length to test which has the lowest resistance and which is the most practical, we are using the same circuit as we used earlier in our experiment except this time is the length. We tested 6 different lengths from 10cm going up in 10 cm to 60 cm.
We also kept the voltage on 2 volts; our results were as followed ….

After taking these results we realised that there should have been a correlation between the length and the resistance, that is that the longer the wire the greater the resistance. We repeated the experiment and exchanged the variable resistor for a different one, after doing this we got these results …..

This time the results showed a correlation between the length and the resistance. This means there was a problem with the variable resistor as this is the component we changed.

Final Testing

We will now test every centimetre between 30cm and 40cm as between these lengths it is the least resistance yet most practical. We will repeat this experiment to find the resistance 5 times as it needs to be very accurate and precise.

If we were to repeat our experiment we would use an analogue voltmeter to make our results more accurate.

Averages

31cm – 0.13+0.13+0.14+0.08+0.08÷5=0.496
32cm – 0.13+0.13+0.15+0.08+0.08÷5=0.506
33cm – 0.14+0.13+0.14+0.16+0.08÷5=0.586
34cm – 0.14+0.13+0.16+0.16+0.16÷5=0.622
35cm – 0.21+0.13+0.16+0.16+0.14÷5=0.688
36cm – 0.14+0.13+0.14+0.16+0.16÷5=0.73
37cm – 0.21+0.13+0.16+0.16+0.16÷5=0.0.702
38cm – 0.14+0.3+0.16+0.14+0.14÷5=0.768
39cm – 0.21+0.5+0.16+0.14+0.14÷5=1.036


Interpreting Data-

Graph to show Resistance against SWG for Constantan Wire (Multimeter)

The results shown in this graph were gathered by using a multimeter as they were a little bit more accurate than the ones gathered by dividing voltage by current. This graph showed a strong positive correlation – The greater the SWG the greater the resistance. This correlation becomes weak as the diameter increases; this is because the greater resistance the greater the temperature and ohms law does not apply when it is hot. This is the explanation for the outlier.

Graph to show resistance against length

The results shown in this graph were gathered by dividing voltage by current. This graph shows a very strong positive correlation, also not all of the results fit the line of best fit the furthest one away from it is 0.02 out of 0.4. This graph showed us that length does not have much of an impact on the resistance of a wire.

Graph to show resistance against wire

From this graph I was able to gather that Nichrome has the greatest resistance and copper the least. This was vital because I was able to choose which wire to use in my experiment.

Evaluation

For me this Experiment was overall very accurate and reliable. Throughout the experiment I did not face many practical difficulties but one was when I came to my final testing, I had to cut the wire I was using down by 1 cm and using wire cutters 1 cm wide that was quite difficult. My method for overcoming this was to measure one cm on the wire by using a ruler and marking on the wire every 1cm, this helped a lot as I was able to see more clearly were the wire was actually being cut therefore making our results more accurate.
Another practical difficulty I had was measuring the wire at 50-60 cm this was because it had been wrapped as coil and so straightening it out to get the most accurate measurement was difficult. To measure the wire accurately we attained a piece of equipment similar to a ruler but at each end a couple of slots to slide your wire through and a knob underneath the ruler to wrap the wire around. After using this piece of apparatus measuring the wire became much easier.
Most of the apparatus I used in the experiment was accurate and working fine apart from a couple of things which could have been improved. One of these was the voltmeters and ammeters I was using throughout the experiment as I was limited to only two decimal places it was much harder to get accurate results and especially a correlation between length and resistance. As the ammeters and voltmeters were digital this is why I was limited to only two decimal places the obvious way of gathering more accurate results was switching to analogue, unfortunately there was no analogue apparatus available, and so we had to make do with digital. Another problem with apparatus I had was the resistor on one of my set of results, when I had gathered the results from that resistor on SWG there was no correlation what so ever this put me back around 20 as I couldn’t figure out why there was no correlation. The next day I came in and repeated the experiment with a different resistor and I had a correlation between Resistance and SWG, this also showed the variable resistor I had recently used was faulty.
The results I had gathered throughout the experiment were generally as accurate and reliable as they possibly could be this is because after each reading I repeated it again 3 times. The readings on the graphs I have produced are close to the line of best fit apart from one outlier on a resistance against SWG graph, the reason for this is because of the heat at which it was when taken and ohms law does not apply in hot conditions.


Conclusion

For my wire I would like to you constantan wire with an SWG of 18 and a length of 35 cm. This is because the data I have collected suggests this will have the least resistance making it efficient and it is also a very practical length and diameter. I have the upmost confidence in the accuracy and reliability results and data I have collected and the only weakness is the lack of accuracy I received from the ammeters and voltmeters, but even with this weakness I still managed to get a correlation in the final test of my experiment. Another reason I have confidence in my results is because of the precision I made sure of in my testing, with this precision and correlations in all of my graphs I consider my choice of wire to be a successful choice. If I could have collected any more data in my tests it would be the choice of diameter in my wire. As I only had 5 to test a greater range in the diameters I had to choose from would have improved the accuracy of the final wire chose.