This is how my experiment will be set up:
My equipment will be:
- Powerpack
- Ammeter
- Voltmeter
- 6 wires with crocodile clips
- 28 swg constantan
- Scissors (to cut constantan)
When we complete our experiment we have decided to go up in 10cm intervals because this is the smallest interval we can use that makes a significant change; also we decided to start at 10cm and finish at 100cm and so there are only 10 measurements for each time we obtain results and as we will repeat this 3 times for accuracy we will not run out of time.
This is how we will work our experiment:
- We will set up the equipment as in the diagram
- The powerpack will be set at 6 volts
- Each wire will have 1cm added to the length to compensate for the width of the crocodile clips (0.5cm x 2 = 1cm)
- A new wire will be used each time
- The wire will always be constantan (28swg)
My prediction is that as the length of the wire increases so will the resistance. I have decided this because the electrons have to travel further when the wire is longer and more atoms get in the way of electrons travelling and therefore the resistance of the wire is higher.
Also I know that the resistance of a conductor is directly proportional to its length. From this I know that the resistance of 20cm wire should be double the resistance of the 10cm wire and the 40cm wire double that of the 20cm wire, etc.
After obtaining my results from the experiments I plotted 3 graphs showing these and also another graph showing the average results.
After looking at my results I believe that all 3 of my experiments were successful and I can see that as I said in my prediction, the resistance through the wire is directly proportional to its length. When looking at my table of results I can see that if the length of the wire is doubled, so is the resistance.
After looking at my results from the experiments, I believe that the results are satisfactory enough to show the relationship between length of a wire and its resistance through it.
Whilst analysing my results I noticed an anomaly on the third experiment on the 40cm length. Here the resistance is quite a bit higher than the line of best fit on the graph. My ideas for what possibly caused this increase in resistance are that the wire could have got hot and then the measurement was taken, meaning that the resistance was higher. Another possible cause could have been from the wire being wrongly measured and too long, meaning the wire’s resistance would be increased. To stop this happening I would make a few changes to the experiment to improve accuracy:
- first of all I would measure the wires twice to ensure exactly the required length
- the measurements should be taken 5 seconds after the power has been switched on, then the wire will not have enough time to heat up (affecting results)
all data will be taken at the relative same time
My results were in my opinion measured to the highest level of accuracy given the apparatus we had available to us. The most important change which would affect our experiment would have to be the powerpack, which although being set on 6 volts, when we had to use a different powerpack, the voltage would be different by up to ½ a volt more or less, although this does not affect the resistance when worked out. If any anomaly occurred it would be easier to spot because you could look back at the bare information and it would “glare”.
Therefore, if I repeated my experiment, in order to achieve more accurate results to show that if length is doubled so is the resistance, I would:
- Use more accurate measuring equipment
- Use a more accurate power supply
- Measure the wire twice to check length
- Repeat the experiment more time to increase accuracy
