Method
To carry out the experiment I need to make sure I make it as fair as possible. I will only be changing one input variable. This will be the length of the wire. Any other variables such as temperature will be kept the same. The current will be kept the same and it will also need to be low so that the wire does not get too hot as it could cause a safety issue. The thickness of the wire and the equipment used will all be the same for all my experiments. I will set up the equipment as shown below and I will record 3 sets of results from the multi meter when set on ‘ohms’. I will attach crocodile clips to the ends of the length of wire I require and then connect these clips up to the multi meter. For each length I will take 3 sets of results and then work the average out. Then, to out rule the chance of the multi meter being inaccurate, I will measure the amps and voltage of the wire for each length and then work out the resistance using ohms law.
Ohms Law
Ohms Law is the law that states the electric current I flowing through a given resistance R is equal to the applied voltage V divided by the resistance or I= V/R. This also means I can find resistance by dividing Voltage by Current.
Equipment/Diagrams
The equipment I will need is the following:
- Multi meter
- Ruler
- Wire
- Ammeter
- Volt Meter
- Crocodile clips
I will set the equipment up as shown below:
Multi meter
Ohms Law
As I have said, I need to take 3 readings using the multi meter and 1 using ohms law. I will work out the average of the 3 readings from the multi meter and then use this average along with the ohms law readings to create a final average for each length. This should be fair and accurate. I am going to take readings for lengths from 10 to 100, going up in tens.
Results
Multi meter
Ohms Law
Complete Results
Conclusion
My results may not be entirely accurate because of the fact that I was manually measuring the lengths out and I could of easily made a mistake. The positioning of the crocodile clips may also have added or taken away a few millimetres due to the width of them.
My early prediction of the resistance increasing in proportion to the increase of the length of wire was right. On average the resistance increases by 0.3 ohms for every 10cm that the wire increases.
The graph backs this up and shows a steady rise, however also shows inaccuracy, as the line does not go through the origin. I also did not include the last set of results at 100cm length on my graph, as this is also clearly inaccurate.
Evaluation
I believe that the inaccuracy of some of my results was due to a mixture of human error and poor equipment conditions. The wire was consistent enough to maintain an equal amount of resistance for every 10cm of length added. However the incorrect results I think were due to possible added resistance from elsewhere, for example the crocodile clips or the multi meter itself. If I were to do the experiment again I would first set up a pre experiment test, using the same equipment and to see if the positioning of the crocodile clips has any effect on the results. I would expect the optimal place would be on the outside of the lengths. I would also make sure that my measurements are all accurate and precise so that I can hold no blame and the only problem would be the equipment.
