I feel my investigation was reliable because I took three repeats (as well as readings each minute for ten minutes) and you can see from the table that the range of temperature rise over these three repeats for each time is never more than 1°C. Therefore I think my evidence is sufficient enough to support a firm conclusion, if I carried out the investigation again under the same conditions I would probably obtain vary similar results. There is also the point that there is little scatter on the graph and I can conclude that there are no anomalies. Perhaps one reason why there is a slight scatter is due to the stirring. Although this did increase reliability by preventing convection currents, I could not guarantee that I stirred for exactly the same length of time and with the same speed each time. Although this would not have altered my results drastically, if one minute I stirred slightly faster than another, this could’ve increased the amount of energy that the water particles had, so the average temperature of the water particles might have been slightly higher.
Therefore, to improve my procedure if I carried it out again, the main change I would make would be to use a mechanical stirring machine that could stir at the same speed consistently throughout the investigation, making my results more reliable. Also, by looking at the table, you can see that the starting temperature was slightly higher on the second and third repeats than on the first. Although this didn’t affect the actual graph because I used temperature rise on my y-axis, it could have been like this because maybe the actual beaker had not cooled from the time before (even though I tried to rinse the apparatus so it had cooled fully, I had a time restriction throughout the investigation so cooling the apparatus was a rush). If this was the case, throughout the first couple of minutes, this could’ve contributed to warming the water and this may have affected my results. Therefore, I would also improve my procedure by allowing longer for my apparatus to cool.
In order to find additional relevant evidence for my investigation, I would vary the power instead of time (because energy = power x time) and see how this affects the temperature rise of water. To vary power I would change voltage because power = voltage x current. I would use a range of voltages from two volts to twelve volts, changing the voltage at two volts intervals so that there are six readings, which would be a suitable range. I would vary voltage on the power supply and take three repeats for each reading to keep my results reliable. In the same way as the experiment I have just carried out I would measure the temperature rise of water in a beaker with a thermometer and I would keep all the other variables (volume of water, size/shape of beaker etc) the same. I would also keep the time variable constant at seven minutes (I feel this is suitable because it should be long enough to see a substantial change in temperature even at low voltages). To prevent convection currents I would use a mechanical stirring machine that would stir at thirty second intervals at a consistent speed (more reliable than stirring by hand) as well as the same apparatus as with the investigation I have just done (electric immersion heater, beaker, clamp stand, digital voltmeter, digital stop-clock, ammeter, power supply, heat resistant mat, thermometer with degree C markings, five wires, boss and 100ml measuring cylinder). I predict that if I carried out this investigation, I would obtain the same ‘S’ shaped curve because at first the electric heater itself would be heating up; then there would be a linear relationship (as the voltage increased, the power would increase so the energy would increase i.e. the water particles would be warmer); then lastly, the graph will begin to curve if the temperatures are high enough due to methods of heat loss.
