Prediction
I predict that if the length increases then the resistance will also increase in proportional to the length. I think this because the longer the wire the more atoms and so the more likely the electrons are going to collide with the atoms. Furthermore, doubling the length of the wire will result in double the resistance. This is because by doubling the length of the wire one is also doubling the collisions that will occur, thus doubling the amount of energy lost in these collisions.
Apparatus
1.5m constantan wire
Crocodile clips
Ammeter (0-5A)
Voltmeter (0-10V)
Power Supply
Connecting leads
Metre rule
Method
1. 1.5 metre length of constantan wire is fixed to a metre rule.
2. The first crocodile clip is clipped to the wire at the 0cm position on the metre rule.
3. The second crocodile clip will be clipped onto the relevant position depending on the required length of wire. The readings will start with 1.5 metre decreasing by 0.1 metres each time, the final reading will be 0.1 metres
4. The power supply is turned on. The voltage and current are then read off the ammeter and voltmeter, then recorded.
5. The power supply is then turned off and ohms law is used to find the resistance (R=V/I). The second crocodile clip is then moved to the next position.
The above steps are completed for each length and then the entire investigation is repeated three times for accuracy.
Safety
Whilst doing the investigation, it is important to keep safety into consideration. Before using the power pack, the pointer should point at 0 volts. It is important to be careful while using the power supply. While handling live wires, it is essential to be careful. The voltage should be kept low because of the safety factor and the wires heating up. Lengths lower than 10cm will not be tried, which also helped to avoid overheating.
Fair Test
In my experiment I am only changing one factor which is the length of the wire. To make my experiment a fair test I will keep the following factors the same:
- I will keep the surrounding room temperature the same or the particles in the wire will move faster and this will therefore have an effect on the resistance.
- I will also keep the material of the wire the same as different materials have different conductivity. This factor will be kept the same by using the same wire all of the way through the experiment.
- The current that will pass through the wire is to be kept the same also. If this is changed the temperature of the wire might change in a way that is not constant making the results incorrect.
- The thickness of the wire. This will be kept the same by using the same wire throughout the whole investigation
Results
Experiment 1
Experiment 2
Experiment 3
Average Results
Before writing my conclusion, evaluation and analysis I would have to consider:
- Whether the evidence is sufficient to enable firm conclusion to be drawn
- The reliability of results
- Reasons for anomalous results and to object such results where appropriate.
- Improvements to the methods that have been used.
- Future investigations to test conclusion
Conclusion
I have concluded that the length of a piece of wire affects the resistance of the circuit. From my results I can safely say that my prediction was right. The resistance did change in proportion to the length. This is because as the length of the wire increased the electrons that made up the current, had to travel through more of the fixed particles in the wire causing more collisions and therefore a higher resistance. The material of the wire and the thickness of a wire could also affect the resistance of a wire. These factors did not effect the resistance in this experiment because they were kept the same. Maybe in the further investigations I could investigate which other factors effect the resistance of a wire.
Evaluation
Generally I think that my investigation went well. Still I feel that I could have done many things to improve the accuracy of my results. In some occasions I feel that I could have done various things to make my experiment a fairer test. I could have repeated the experiment a couple more times. I could of experimented with more lengths and decrease the range between each length. I could have concentrated more during measurements and not get distracted by peers. I think that my results were quite accurate. If I were to repeat this experiment I would change the variables and try investigating other aspects that could effect the resistance of a wire. For example how the density or mass of a wire affects its resistance. I could also investigate how different types of wires affects its resistance. In the future I would also like to investigate how voltage and current affects the resistance of a wire although this type of experiment can be very dangerous.
Analysis
During my investigation I came across many minor errors, which could have affected the accuracy of my experiments. These errors were measurements. The length of the wire could have been plus or minus 1cm. This could be because we would have to consider the efficiency rate of the length of wire measured. The size of the voltage or current measured could have been plus or minus 1 amp or volt. This is due to the accuracy of measuring the voltage and current at its peak and the judgement of the value. Many of these errors are down to the accuracy of human judgements. If I were to repeat this experiment I would consider these errors and try to concentrate more when measuring. Despite the errors made in this experiment my results were reliable. I noticed some patterns in my results. I have noticed that as the length of the wire increases the voltage increases and the current decreases. This is because the resistance of a wire is proportional to its length. Although there are more vibrating positive ions in a longer wire to impede electron flow, there are also more free electrons, so the effects should cancel out. But, at constant voltage, less energy is available to the electrons to move through each centimetre of wire. This means that the electrons move more slowly, so fewer pass a given point in one second. Hence the current, which is rate of flow of charge, is reduced and the resistance increases. I have gathered this scientific knowledge from the ‘Heineman Double Award Physics For OCR A’ textbook, authors: Sandra Mitchell and Chris Sherry.
