I obtained this information at:
Carbon is also one of the only non metals that conducts electricity
Experiment:
In the preliminary experiment, I was trying to measure the current passing through carbon putty to see if there was any pattern I could investigate between resistance and length of carbon putty. I used a power pack set on two volts connected the putty as shown in the diagram, varied the length from 10.5 to 11.5 cm keeping the diameter constant at 2.2 cm. I used the ammeter setting of a multimeter to measure the potential differences passing through the conductive putty. This gave me the following set of results:
Using the following formula R= V/I I was able to work out the resistance of the putty at these lengths. Below are my results:
These readings clearly show a pattern in that as we decrease the length of the putty, the potential difference gets bigger and the resistance decreases. What can also be seen is that from a length of 14.5 cm where the resistance was 16.5 ohms to a length of 7.5 cm where the resistance was 7.7 ohms the resistance has almost halved. This process was very time consuming, as we had to first measure the current and then calculate the resistance. As we were also provided with an Ohmmeter I decided to measure the resistance directly.
Investigation:
I am investigating the length of the carbon putty as this factor is connected to the physical effects of the putty. It is much harder to record the temperature of the conductor than to measure the length of the carbon putty. And the experiment to investigate this factor should hopefully give a good straightforward result.
Prediction:
I predict that as I increase the length of the putty the resistance will also increase. From all the information collected in my preliminary work I predict that as I double the length of carbon putty the resistance will also double
Safety:
I ensured this was a safe experiment by:
- I wore gloves at all times when handling the putty and objects that had touched the putty. This was because the putty is toxic.
- I washed my hands after every experiment to remove possible traces of toxic putty.
- I made sure that the power pack was switched off between experiments.
- I made sure our hands were not wet when handling the power pack and other electrical equipment.
- The putty was capable of reaching high temperatures when a large current was run through it, I made sure that the putty was cool enough to handle after contact with electricity.
- We were given a knife to cut the putty with, we handled this with care.
Control of variables:
My variables were:
- Diameter of putty, which we tried to keep at 2.2 cm by evenly rolling the putty.
- Temperature, I know that this affects resistors and therefore was careful to carry it out at room temperature. As the rooms are air-conditioned I am assuming that this temperature was constant.
- I kept the voltage the same by using the same stetting on the power pack.
- I ensured that the copper electrodes did not sink into the putty.
Apparatus:
- Carbon Putty
- 2 pieces of thin copper
- Crocodile clips
- Wires
- Ceramic tiles
- Rubber gloves
- 2 Multimeters
- Knife
Method:
To measure length
1.Roll the carbon putty to the diameter wanted with 2 tiles into a long sausage. Make sure that the diameter is uniform all along.
2.Measure the diameter and record it.
3.Cut the carbon putty to the length wanted
For the experiment
1.Place the two pieces of copper at each end of the putty (this ensures a fair test)
2.Attach crocodile clips at each end of coins.
3.The power pack will be kept at a constant 6 volts
4.Measure the resistance
5.Repeat experiment thrice again to ensure a fair test
The setup of the experiment will be identical to my preliminary experiment. Because the putty was toxic and very messy we used gloves when handling it, also when subjected to high voltages the putty became extremely hot and care had to be taken when picking it up.
Results:
These are my results for my experiments, I have also drawn graphs for resistance and average current.
Analysis:
Analysis:
What I found out from this experiment is that if you increase the length of the putty the resistance to the same voltage increases.
Graph 1 illustrates that the resonate of the conductor varies with the different lengths of the conductor. It shows a positive correlation because as the length increases so does the resistance. However as is shown by the - - - - - line I have drawn on the graph, it does not pass through the origin and therefore the relationship is not a totally proportional one. This graph also appears to reach a point on the graph where it levels off when I draw in my line of best fit. This point is reached at 12 cm in length.
My prediction that the resistance would double as the length of the putty doubled was nearly correct. From the table it can be seen that as we double the length we have roughly doubled the resistance. For instance when we doubled the length from 2 cm to 4cm the resistance went from 2.8 to 4.33 ohms a difference of 1.5 ohms which is almost half of 2.8 ohms. From 4 to 6 cm the difference was 1.46 ohms which is more than half of 4.33 therefore the pattern is beginning to break down. However, between 6 and 8 cm there is a difference of 2.54 ohms and the pattern re-appears. As I noticed in my graph the resistance appeared to level off as the putty got longer and this is borne out by a difference of only 0.35 ohms between 10 and 12 cm.
Conclusion:
From my experimental evidence I can conclude that there is a definite relationship between the length of carbon putty and its resistance to electricity. The longer the wire the greater the resistance. Graphically this appears to be an almost directly proportional relationship although some of my results appeared to be anomalous
Evaluation:
What I found out from this experiment is that if you increase the length of the putty the resistance to the same voltage increases.
Graph 1 illustrates that the resonate of the conductor varies with the different lengths of the conductor. It shows a positive correlation because as the length increases so does the resistance. However as is shown by the - - - - - line I have drawn on the graph, it does not pass through the origin and therefore the relationship is not a totally proportional one. This graph also appears to reach a point on the graph where it levels off when I draw in my line of best fit. This point is reached at 12 cm in length.
My prediction that the resistance would double as the length of the putty doubled was nearly correct. From the table it can be seen that as we double the length we have roughly doubled the resistance. For instance when we doubled the length from 2 cm to 4cm the resistance went from 2.8 to 4.33 ohms a difference of 1.5 ohms which is almost half of 2.8 ohms. From 4 to 6 cm the difference was 1.46 ohms which is more than half of 4.33 therefore the pattern is beginning to break down. However, between 6 and 8 cm there is a difference of 2.54 ohms and the pattern re-appears. As I noticed in my graph the resistance appeared to level off as the putty got longer and this is borne out by a difference of only 0.35 ohms between 10 and 12 cm.
Conclusion:
From my experimental evidence I can conclude that there is a definite relationship between the length of carbon putty and its resistance to electricity. The longer the wire the greater the resistance. Graphically this appears to be an almost directly proportional relationship although some of my results appeared to be anomalous
Evaluation:
I think that my experiment went quite well as I was able to produce quite accurate data and my graphs showed a definite pattern and I was able to use the results to draw a conclusion. The procedure I used was a simple one and the equipment was easy to manipulate.
I think that on the whole the readings that we took were fairly accurate and we ensured their accuracy by repeating the experiment three times. When I look at my table of results I can see that my repeats were all very close. I did expect to see a pattern emerging concerning the length of the putty and if you look at my graphs it can bee seen that the readings for 6 cm and 10 cm do not lie on the curve. These could therefore be termed as outliers or anomalous results. This could be due to several errors which could have been made.
One error with this experiment is that the wire that connects the putty to the Power pack has its own resistance and this could have affected results. We tried to overcome this by always using the same wires, and therefore this fault was built into the system. Another error that could have occurred is the fact that the diameter of the putty was achieved by hand rolling it. This could have led to un-evenness due to different hand pressures and could also produce air bubbles.
I would like to extend this experiment by checking the resistance of putty at both above and below the length used in this one to see if the graph I have drawn is accurate. This would be above 12cms and below 2cms.
If I was able to further extend my experiment I would like to change the diameter of the putty and see if this made any difference to the resistance. I could use both thicker diameter than 2.2cm and/or thinner than 2.2cm. This would enable me to compare all the results and see if the pattern held true for all thicknesses of putty. I could use a Kenwood mincer or a spaghetti maker to ensure that the putty was the same diameter all along its length. .
