- Material - Thirdly, the material used would be a factor. If the material being used contains atoms with a large number of electrons on the outer shells, then this means there are more electrons available. That means that a material with a large number of electrons in the outer shell should have less resistance. If the atoms are more closely packed, it will be harder for the electrons to flow through the material and this will cause the resistance to be increased.
Prediction and Hypothesis:
I think as you increase the length of the Constatan wire, there is also an increase in the amount of resistance. The current is the flow of electrons; the current is dependent on the amount of voltage, which is applied. Voltage is the push given to the current. The current has to go through a circuit, which contains resistance so if you increase that push you also increase the flow of the current. All materials have a slight resistance to electricity factors affecting the resistance is: Length, Voltage & Temperature and Surface Area.
Apparatus:
- Power Pack - Meter Ruler - Crocodile Clips
- Constatan wire - Ammeter - Sellotape
- Leads - Voltmeter
Circuit Diagram:
Method:
Firstly, the circuit should be set up as shown in the diagram above.
A length of wire over a mater and a half long is sellotaped to two attached meter rules. The positive crocodile clip is attached at point 0cm, and the negative one is moved up and down the wire. It will stop at the points 100cm to 10cm, stopping at all the 10cm in between. Each time reading the digital ammeter to work out the resistance R=V/I (Resistance = Voltage ÷ current).
Other variables voltage, thickness and temperature will be kept constant, although the temperature will rise once a current is passing through it, which will cause the atoms in the wire to vibrate, and so obstruct the flow of electrons, so the resistance will increase and cause a small marginal error.
It is important that there is no room for error in this investigation, so special procedures will be taken. Firstly, the experiment will be repeated four times to help find the averages in case a reading is not accurate. Also, the same wire will be used when reading the currents as we move the crocodile clips down from 100cm to 10cm. A Constatan wire is used because it does not heat up as much as copper will, so the resistance is not effect so much. Digital ammeters will be used to read off the currents, as it is more accurate and more precise in its measurements compared to that of a normal analogue ammeter.
Preliminary Experiment
We carried out a preliminary experiment to see the other factors that could affect the experiment and also to see if we could improve any of the steps in the method. We found that the copper wire gave anomalous results, so I have now chosen to use the Constatan wire instead. I found that if I decreased the voltage, then the wire would not start to burn, and affect our results, so I chose to keep a lower voltage setting, although a little higher than in my preliminary experiment. This will give me a more spread out range of results to compare.
Results #1: Preliminary Experiment -
Copper wire was used during the preliminary experiment:
The table above shows the results given in the preliminary experiments. The results do not range greatly, and it is difficult to comment on the results. The actual experiment will need to use a higher current to obtain bigger figures, so that it is easier for me to comment on. But, the current cannot be too big; otherwise it will burn the wire and affect the results. However, Constatan wire is better under higher currents and therefore should produce more accurate results for me to use.
Results #2: Actual Experiment –
Constatan wire was used during this experiment:
These results above are going to be the results that I am going to be using for my analysis and evaluation. I have made all of the improvements suggested from the preliminary experiment, and I am now going to plot these results into a graph and comment on the results that I have obtained.
Conclusion
In my prediction I said that if the length of the Constatan wire increases than the resistance would also increase in proportion. From my graph I have shown that my prediction was correct, as the ‘Line of Best Fit’ is a straight line proving that the resistance of the wire is proportional to the length of the wire.
The length of the wire affects the resistance of the wire because the number of atoms in the wire increases/decreases as the length of the wire decreases/increases in proportion. The resistance of the wire depends on the number of collisions the electrons have with the atoms in the wire. So, if there is a larger number of atoms, there will be a larger number of electrons colliding, which will increase the resistance of the wire.
For example, as the length of the wire decreases by half, then the resistance increases by half in proportion. If the wire was to triple in length, then the resistance will decrease by triple in proportion again.
Evaluation
From my results table and graph, I can see that the results I collected were very reliable. I can tell this, because my results table does not show any individual anomalous results. This means that I did not have to leave any results out of my averages, because they were anomalous. Also, on the graph I can see that none of the averages plotted are anomalous, because all of the averages lie either on, or close to the ‘Line of Best Fit’.
But, to improve my investigation, it could have tested the resistance with a different material wire, or the same wire but at different thickness’ to see whether the resistance is greater or weaker due to there being more atoms in the same length of wire. Also, more readings could have been taken, i.e. every 5cm rather than every 10cm, so that it could me more to comment on and would be a more accurate way of testing my prediction. I could have also taken down more readings for each wire length to find a better average and in case there were some anomalous results, which would give room for error.