Prediction
I predict that if the length of the wire increases then the amount of resistance in the wire will also increase. I think that the resistance will increase proportionally to the increase in length of the wire. I think this will happen because the longer the length of wire the more atoms there are and this means that there is more chance of a collision. If a length of wire is 5cm long and the resistance was 1.5 Ohms then if the length was doubled the resistance should double to about 3 Ohms. This is because there will be more collisions. When I plot my graph of results it should show that length is proportional to resistance.
Equipment
To carry out this experiment I will need:-
- A power pack set at 2 Volts
- 100cm steel wire attached to a metre ruler
- Ammeter
- Voltmeter
- 2 Crocodile Clips
- Connecting wires.
Circuit Diagram
Preliminary Work
For my preliminary work, I set up the experiment according to my method and took some readings. It helped me to realise any mistakes that I was making which may affect my real results in any way. These were things such as turning the voltage too high, which would be quite dangerous and could have burnt the wire or the laboratory desk or damaged the power pack. I also took readings from the ammeter and voltmeter too quickly and did not allow time for the value to settle before recording the result. This would have only made a marginal difference to the results but the accuracy is the main part of this investigation and I wanted to ensure that my results were as accurate as possible, this shows that I need to be a bit more patient when taking my real readings. I also need to ensure (although it was not a problem during the preliminary test) that the crocodile clips are set at exact points i.e. 10cm or 50cm to make readings more reliable and exact. One other thing that I noticed was that the independent variables do not increase or decrease to make my results unreliable. I need to ensure that the voltage is kept constant and that I keep the temperature as constant as possible although it will fluctuate with extended current flow. I cannot do much to control this variable except ensure that the power pack is switched off after each reading has been taken.
Safety Precautions
Throughout this experiment, I made sure that safety was one of my main priorities. I was extremely cautious when measuring the voltage and current of the wire in case the wire became very hot. I didn’t wear a lab coat as it was not easily identifiable that I would need one and goggles were not worn as the voltage was not increased above 2 volts and there was a very low risk of any sparks would be produced during this experiment.
Method
I firstly will plug the power pack into a socket. This is the most important piece of equipment in this experiment and it is the one that I will ensure that the voltage will be kept constant. I will then connect 2 wires that lead from the power pack to the ammeter and a second wire to the voltmeter. From the ammeter a crocodile clip was connected with the other end connected to the meter wire at 0cm. This will remain here as it is simply reading the current from this point whilst the other wire from the voltmeter varies along the wire. The crocodile clip from the Voltmeter is connected at 20cm and this will be repeated at 30, 40, 50, 60, 70, 80, 90, 100cm. The ammeter will remain at 0cm to record the variables easily i.e. the value from 0cm to the recording value does not need to be calculated. The voltage on the power pack will be set at 2 volts and the recordings will be taken three times at each length. Then the resistance will be calculated using the R= V/I formula.
Fair Testing
To ensure that my experiment is fair test, I have to ensure that everything is kept the same throughout. I need to make sure that sure that all the factors and variables which may affect the eventual results are kept the same to avoid human variation. These are things like temperature, which can affect the wire, either by the heat in the laboratory or the voltage running through it. To combat this I am going to ensure that the power pack is switched off after each individual reading to prevent the voltage heating the wire up. This in turn should increase the reliability of my results at each value. I am also going to ensure that the wire is always kept the same and ensure that the crocodile clips are placed on the exact points on the wire and I will ensure that I read the volts and amps correctly.
I think that these are important factors because it can be decisive as to how accurate the results are in my experiment.
Reliable Results
To make certain that my results are reliable, I will take the readings of each length three times. This means that there will be three sets of data for voltage, current, and resistance all from 20cm to 100cm. I will then calculate an average and put this into a separate table and graph.
Sample Results Table
Observation
For this particular experiment, I found that there is no blatant observation to be made i.e. observing a reaction or change take place. However, there is one observation that can be made and stated which is taking down the readings from the ammeter and voltmeter. I will then simply look and write down the values of the voltage and current and use them to calculate the resistance.
Results
As I stated earlier, I am going to record three sets of data and then calculate an average for the data. Below are my three tables of results and my table of averages.
Set 1
Set 2
Set 3
Average Results
Graphs of Results
Analysis of Results
From the Tables above, I can see that resistance in a wire increases as the length increases. This is with 2V running across the wire. An example of this can be seen at 20cm where the resistance is 5.61 ohms (average but further along the table the resistance at 80cm is 22.87 ohms (average)This is an increase off 17.26 ohms. This proves that as the wire becomes longer the higher the resistance also becomes.
Analysis of Graphs
Graph 1 shows the resistance across a 2V steel wire. I can see from the graph a clear trend. The resistance in the wire is increasing almost directly proportionate. I drew a line of best fit to prove that this is true.
The graph of the resistance calculated for set 1 is not as good as the graph lines for sets 2 and 3. This is because the results were not measured as accurately as they could have been. There are a few anomalies in all of the lines but especially the line for set 1.
My averages graph is more accurate than the others as this is the overall result. I drew a line of best fit and calculated the gradient. This was to find out the steepness of the graph and find out if a conclusion is to be made from the results. To work out the gradient I calculated the change in resistance and the change in length. Then I did this calculation.
Gradient= Change in resistance/ Change in length
Gradient= 24.4/80
Gradient= 0.31
Sot he gradient of the 2V steel wire averages graph is 24.4/80= 0.31 (2dp)
So from the calculation of the gradient and the graph it can be seen that the resistance almost doubles.
Conclusion
From my results, I have come to the conclusion that if you increase the wire length, then you increase the amount of resistance in it as well. The resistance of the steel wire at 2V increase almost in proportion to the length. I think that this was because of an increase in the amount if atoms in the wire at each ascending length and so if there were more atoms (that were moving with a lot of energy from the voltage across them) then there would be many collisions between them and the electrons therefore causing a lot of electrical friction hence resistance.
Linking Prediction to conclusion
My original prediction was that increasing the length of a wire would increase the resistance across it. And, from my results I can see that this is true because at 20cm the resistance is 5.61 Ohms (average) and at 100cm it is 30.01 (average) Ohms- a difference of 24.4 Ohms. This proves that the resistance is increasing as the length is increasing.
Evaluation
I think that my experiment has been a successful one as my results supported my prediction. My results were particularly accurate as each reading at each length was taken 3 times. I also calculated an average of my resistance which I had found using the formula V/I. There were a few slightly strange results (anomalies) but not large mistakes which would have affected my overall averages. I think this was because of the caution that I took to ensure that the equipment was set up correctly with careful measuring of the length that the second crocodile clip was on.
However, I think that I could have repeated my results more for the reason that the most accurate results can only be achieved by constant repeats which I did not show in my experiment. This was because the time allocated did not allow for me to do so and I believe that as an improvement of what I would do if I did the experiment again, I would have to say that, with more time, I would also repeat the results further for even more accurate and reliable results. I would also take even more caution when recording the values because although I did my best to turn the power supply off at during this experiment, even a delay of 30seconds could increase the temperature of the wire and make my set of results not as accurate as the last set. This was very important as temperature was one of the possible variables that I wanted t keep constant so feel that I could have been more aware of when I was recording the value that the power pack was definitely off.
I believe that I could have improved the method by making it more specific. I stated clearly all the various methods I took in setting up but I could have been more specific about how the apparatus was used and why. I certainly could have explained my experiment step by step with numbers explaining carefully in which order everything needed to be set up.
I believe that I did get a suitable range of results for my experiment. I recorded values between 20cm and 100cm. I did not measure the resistance at 10cm because the resistance would have been too high and there would have been a risk of the power pack short circuiting. I think 20-100cm is a very good range of results because I can see if there were any clear trends in my results. I could say however that I could have recorded lengths at 20cm, 25cm, and 30cm and so on to make my results even better ad more accurate. However, I feel that my range of results was good enough to be able to confirm a pattern in my results, as I certainly believe that my range of results was a good one.
Other areas in the experiment which I feel I could have improved on were factors like controlling the temperature because although difficult it is a very important factor which can ruin results if not controlled. Measuring the lengths of the wire is also an inaccuracy that could be improved, as the rulers used are not exact it is difficult to get an accurate reading of length by eye, as the wire may not be completely straight and it could be a different thickness at different points along the length. These could well have contributed towards error. These results would be difficult to improve on as they are reasonably accurate and there were only slight anomalies in the results.
Nevertheless, if I were to do this experiment again I would use newer, more accurate ammeters and voltmeters, a more accurate method of measurement and take a much wider range of readings, and more readings so that a more accurate average can be taken.
Overall, this investigation has been a very successful one. I feel my results and analysis have been as accurate as they could have been under the time allocated circumstances. However I feel with extra time, I could have repeated the experiment and made it even more accurate and adapted it to try other variables. These would be things like investigating the effect of cross sectional area or temperature eon the resistance of wire.