Electrical resistance is the effect a wire or component has on a current as it tries to prevent the current flowing through it. The electrons in a wire flow through the wire but there is a chance that they will collide and be slowed down by an atomic nuclei, this is resistance.
The resistance of a length of wire is calculated by measuring the current present in the circuit (in series) and the voltage across the wire (in parallel). These measurements are then applied to this formula:
V = I/R
Where V = Voltage, I = Current and R = Resistance
This can be rearranged to:
R = V/I
This formula only works for objects at a constant temperature.
= Nucleus
= Electrons (current)
The diagram above shows electrical resistance.
Hypothesis
When the length of wire is increased the resistance also increases. When the length of the wire is decreased the resistance of the wire in decreased. I think this because the longer the wire is the more nuclei there is for the electrons to bump into, therefore making their path more difficult.
Preliminary Test
I need to find a safe voltage, which also gives good, usable results.
In the lab we couldn’t reasonably use lengths more than 100cm, as the desks we are working on are just over a meter in length. I am going to use 10cm as my shortest length because any shorter the wire might heat up making the investigation unfair.
Method
- Set up a series circuit making sure the ammeter is in series and the voltmeter is in parallel. (See below)
- Cut 100cm of chosen wire
- Place the wire across the middle and attach with two crocodile clips.
- Take readings every 10cm.
Fair test
I am making the investigation fair by just changing the variable, which is the length of the wire. I am going to use the same copper wire throughout the investigation. I also will keep the voltage the same and keep it at a constant temperature.
Equipment
Power pack
Voltmeter
Ammeter
100cm of copper wire
Crocodile clips
Wires
Safety
In order to perform a safe experiment, a low voltage of 3V was chosen so that overheating was minimalist. Furthermore, lengths lower than 10cm were not tried, which also helped to avoid overheating
Results
Results table
Conclusion
As I predicted, an increase in length resulted in an increased resistance. The wire shows a strong trend of a straight line, i.e. the length of the wire is shown to be directly proportional to the resistance – double the length and the resistance doubles.
Evaluation
Accuracy of results
Length of wire- It is difficult to cut exactly 10cm off the wire each time. It is possible that some measurement may have been slightly out.
Readings- The ammeters and voltmeters tended to fluctuate between a few points making it hard to take a reading.
Temperature-At some points (more likely in the lower lengths), the wire might not have been left long enough to allow it to cool completely so that the temperature may have been higher for the next measurement. Whilst unlikely (due to the three sets of results), this would cause a higher resistance because of vibrating nuclei.
There were no significant problems or difficulties that were encountered when carrying out this investigation. The accuracy and reliability of the results and conclusions are very good. Within the accuracy of the method used, and for the range of values investigated, it is clear that the length of a wire is proportional to amount of resistance in the wire.
Improvements
The procedure used was simple and straightforward and no difficulties were encountered. A small improvement could be made to measuring the length of the wire. Using a rule with millimetres to measure he wire could have made the measurements slightly more accurate. I could have also made sure the wire had completely cooled down after each reading.
More repeats could be taken but I don't think this would add much to the accuracy of the conclusions.
Longer lengths of wire could easily be tried, up to whatever maximum could be obtained. With a suitable location a length of several metres could be obtained. If the wire gets too long then a higher voltage might be needed in order to give good results. It would be interesting to try shorter and shorter lengths although a limit would be reached when the wire begins to heat up. It may be possible to use a lower voltage although readings for longer pieces of wire would not be so good
Extending the investigation
Suggestions have already been made to extend the range of lengths investigated and to see if the observed trend continues. There are alternative wires that can be used. Instead of using copper wire other wires could be used. It would be interesting to investigate how the structures of the different wires affect the resistance. It would be interesting to find out what affect adding components to the circuit would make to the resistance of the wire.
