ANALYSIS
To analyse my results I will extend my table from before by adding 1/v and pv:
p (x105 Pa) v (cm3) 1/v (cm-3) pv (x105 Pa cm3)
3.40 16.0 0.062 54.40
3.23 16.9 0.059 54.58
3.09 17.8 0.056 55.00
2.91 18.8 0.053 54.71
2.78 19.7 0.051 54.77
2.62 21.0 0.048 55.02
2.48 22.1 0.045 54.80
2.31 23.7 0.042 54.75
2.15 25.7 0.039 55.26
1.97 28.1 0.036 55.36
1.73 31.9 0.031 55.19
1.60 34.9 0.029 55.84
1.41 39.1 0.026 55.13
1.28 43.3 0.023 55.42
1.12 50 0.020 56.00
1.03 56 0.018 57.68
Using my table, I can see that as p increases from 2.15 to 3.23, v decreases from 25.7 to 16.9. I can also see that when p is approximately halved from 3.4 to 1.73, v is approximately doubled from 16 to 31.9. To show this is true I will compare two more sets of results:
P goes from 2.78 to 1.41, v goes from 19.7 to 39.1
P goes from 2.62 to 1.28, v goes from 21 to 43.3
Using my extended table, I can see that pv is more or less a constant value. This shows that Boyle¡¦s Law is true because it states that the volume of a fixed mass of gas is inversely proportional to the pressure of the gas as long as the temperature is constant. Therefore, if I plot a graph of p against 1/v and get a straight line then that means that Boyle¡¦s Law is correct, this does roughly happen.
EVALUATION
For my evaluation I will know see what can be improved in the experiment. Firstly, the scales for both the volume and pressure were not sensitive enough. This leads to results being in accurate due to the results being hard to get right. However, this inaccuracy is a systematic error because it would affect all the results. Secondly, when we decreased the pressure the oil did not go down immediately. Instead, it clung to the sides of the tube. This would therefore make the volume lower than it should be and can cause the graphs to be inaccurate. Thirdly, the temperature of the apparatus could have changes towards the end of the experiment. This could explain why the last two results of pv are higher than the rest. Although our experiment did contain inaccuracies, it is accurate enough for a school experiment.
ANOMALOUS RESULTS
The main reason for an anomalous result in this experiment could be a human error. For example, the reading could have been misread or misheard, it could have even been misplotted. Although that would be the main reason, the errors could be due to dodgy equipment, which could cause some pressure to be lost. Another reason could be that during the experiment the tube containing the oil may have heated up, this causes the temperature of the oil to change and it may expand causes the volume reading to be inaccurate.
WERE ENOUGH RESULTS TAKEN?
I think that enough results were taken for a school experiment but not for a professional experiment. For a school experiment, only 10 - 15 results are needed but for a professional experiment 1000s of results would be needed. This is to make sure that no mistakes were made but for a school experiment, we can check our results with past years of the experiment and with results from a textbook. From my results, I can safely say that Boyle¡¦s Law is correct.
CRITICISMS OF EXPERIMENT
There are criticisms of our experiment but they do not affect the general outcome of the experiment. Firstly, the graduations on the pressure gauge were too big to get an accurate result to two decimal places. Secondly, on the volume scale there were only markings for 1cm3; which isn¡¦t very accurate. Thirdly, the meniscus of the oil was hard to see. This would lead to approximation of results and could cause inaccuracies. My last criticism of the experiment is that we should have waited longer between letting the pressure down and taking the result. This would let the oil have time to run down the sides of the tube and give an accurate result.
IMPROVEMENTS
My first improvement I would do is to use digital meters to give an accurate result and then there would be now guessing to get the result. If digital meters are not possible to get, I would then use meters with more graduations. This would give me a more accurate result. I would also increase the pressure instead of decreasing it. This would stop the oil clinging to the sides so the volume reading would be correct. The next thing I would change would be the tube. I would make the tube longer and thinner. This would make the scale more accurate because the smallest of changes in volume would be seen easier. Although we did enough results, I would probably like to do the experiment one or two times extra to make sure I did not get it wrong. Looking at my graph, the last couple of results of pv are the highest, which could be due to the temperature changing. To stop this I would like to keep the temperature of the oil to be monitored to see if it goes up or down. If it did change then we would have to wait until it went back to normal to keep the experiment accurate. My final improvement I would like to make would be to use different gases so we can really say that Boyle¡¦s Law is true for all gases and not just air.
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