To investigate the factors that affect the resistance of a wire.

Equipment:

• Nichrome resistance wire – 32swi 1metre long
• Power pack
• 5 wires
• 2 crocodile clips
• digital ammeter
• digital voltmeter
• meter ruler

Method:

• Get all of the equipment and set up as shown in the diagram
• Keep the power pack at 6volts at all times
• Start off by measuring how much resistance would be needed to flow the electricity through a 100cm wire using the ammeter and voltmeter and using the formula:

R=V

     C

Where R is the resistance (Ω), V is the voltage (V), and C is the current (A).

• Then decrease the wire at a 10 cm constant each time measuring the voltage and current. This is done by moving one crocodile clip along the wire and the other being kept still at 0 on the metre ruler. Use a range of 100-10 cm.
• Record results and work out resistance using the formula
• Repeat the experiment another time and record an average to make the results more accurate.

Diagram

                           

Fair Test: To make this a fair test we have to recognise the factors which will affect the end results suck as temperature. As the temperature of a wire increases so does the resistance and this will happen in this experiment because as the power pack is kept on longer, more electricity will be produced and the wire will get hotter. To prevent this from happening I am going to turn off the power pack between measurements to make the results more reliable. Also when changing the crocodile clips to get the length of the wire needed they might not be exactly the right lengths so to make this more fair I will try to get the length exactly correct so there will be no errors. The investigation will be repeated twice and an average taken so that the results will be more accurate and no obvious anomalies should occur.

Safety

We have to be careful that the resistance wires do not reach too high temperatures. This is for safety and for fair testing and we will also be careful not to touch the wire when it is hot to stop any burns. To stop this we will turn the power packs off between each measurement. Also make sure that all wires are away from the floor so that no accidents happen.

Results

Attempt One

Attempt Two

Average

Conclusion

Overall my results show that my prediction is right. The tables show that as the length increases so does the resistance and this is because there is a bigger surface area for electrons to be produced. Also my tables show that as the voltage increases, the current decreases and this is because as there is a bigger push of electricity from the voltage less current is needed to make it faster so it decrease. My graph shows positive correlation proving that my prediction was right because the graph follows an almost perfect pattern in a positive direction, however does not support my prediction of when the length doubles so does the resistance because to do this the graph must be directly proportional and in this case it is not so my prediction was wrong. The line of best fit on my graph does not show any obvious anomalies so my fair testing must have added to the accurate results. My results would also prove that as voltage increases so does the resistance which is another factor which affect resistance so as you can see by my tables of results that as the voltage increases, the resistance does as well.

Evaluation

The results in all showed a successful investigation as the graph did not show any obvious anomalies apart from one which lie slightly off of the line of best fit but they do not affect the results in any way. The results are quite reliable however I am sure that they must have been affected in a small way because the points on the graph were not all following a perfect pattern. The most common factor that will have affected this is most probably temperature of the resistance wire or the lengths did not follow an exact constant just as I said in the fair testing. To make it more accurate we could have checked the temperature once in a while to make sure it did not over heat and would not affect the results and as with the length it was hard trying to get it perfect as it was hard to see just by the eye and the wire was not properly straight or had a different thickness throughout therefore causing inaccuracy of some results. If we were to do this experiment again we could try to get a straighter wire so there will not be any discrepancies in the results. I only repeated the investigation once which, although did give quite good averages, could have been better if I repeated it more so in that case the graph would show a more consistent pattern and more reliable and accurate results .Also I would test other factors such as thickness and temperature to see if they do affect the resistance in any way.

Overall the results I did get were quite accurate considering the errors of which we endured and we could consider these if we were to do the experiment again in the future to make the results better and more unbiased.