Method:
Once you have fully set up the experiment following the circuit diagram then you need to put the lit Bunsen burner under the tripod with the gauze and beaker of water. The Bunsen should be set with the collar half open to allow a slow but steady source of heat, which allows enough time to take each result. The temperature will now increase on the thermometer and you should take the readings of the current and voltage every five degrees to allow a large set of accurate results, and then stop once you reach 95º, to prevent the water from boiling over.
In order to make this a fair test you need to have only one varying variable and the other variables need to fixed. Your varying variable will be the heat and the fixed variable will be the voltage, current and resistance. Here is a list of equipment that you will need for the experiment:
Health & Safety:
To make sure the experiment is as safe as possible you should take a few safety precautions. Wearing safety goggle until all practical work and clearing up is finished. Tucking in your tie when around a Bunsen burner. Standing up during the experiment and making sure that nothing is on the floor is also very important in case of an emergency. Stools should be under the bench, and when using a Bunsen burner it should be on a safety flame at all times except when in use in the experiment.
Analysing the Data
The best way to analyse the data in this experiment is to plot it onto a graph and put a line of best fit on it. A table of result could also be used for analysis.
I believe this method is practicable because I am measuring the temperature to one degree, the current to one decimal place, and the voltage to two decimal places. Measurements of this accuracy can easily be obtained from the measuring devices available, as they are not too precise, although they are detailed enough to be appropriate for my experiment and graph. To ensure maximum accuracy within the given range you should repeat the whole experiment at least once and then average the results.
Observations:
When I started the experiment the voltmeter showed 2V but throughout the experiment it slowly dropped and by the end it was only at 1.83 this could be due to the internal resistance of the power supply, as more current goes round the circuit the voltage supplied will also drop due to this resistance. From the current increase and the voltage decrease we could work out the internal resistance of the power supply, but were not going to. As the water heated (over 60°C) small bubbles of oxygen were formed on the sides of the glass beaker, which then floated to the top and popped.
When we first put the Bunsen burner underneath the beaker we expected that the temperature would begin to rise instantly. However it took about twenty seconds for the temperature to increase due to the thickness of the glass. If we had used a glass beaker with thinner glass then we would have noticed that the time for the temperature to start increasing would have been less.
Results:
(2 S.F)
Conclusion:
From looking at the graph we can clearly see that as the temperature increased the resistance decreased. However it was not proportionally as the line is not a straight one, but a curved one and so it was exponential. The voltage and the current behaved as expected. The current increased in a linear fashion and the voltage stayed pretty much the same throughout. So from this I can say that it supports my hypothesis.
Evaluation:
Even though we did the experiment twice and averaged our results we still did not get perfect straight lines in our graph, this is because of random anomalies. However the data is still very accurate as the experiment was done twice. To improve our experiment we could have done the following:
- Used an electronic temperature probe connected to a laptop computer.
- Repeated it more times to get a better average
- Used more sensitive reading equipment capable of many decimal places
- Used a heat source, which would supply the energy at a more constant rate.
The procedure that we carried out was done fairly quickly and I think that we could have spent more time doing it and taken more care over obtaining the results.
Final Thoughts:
My final thought is that as my conclusion fully supports my hypothesis then the experiment is a success and everything was followed according to plan. I think that it would have been easier if we had known which type of thermistor that we were using in the practical but we managed to overcome this with a little research and pure intelligence. The graph was easy to produce and the results seem to be very good. The experiment could be repeated but as a replacement for water a liquid with a higher boiling point could be used so that more results could be collected.
