Internal resistance can be affected by many factors. One main variable, and the one I will be exploring is that of temperature. Hypothesis I predict that the temperature rise and increase in the internal resistance will be directly proportional. In ideal conditions, this would be the case , however, we must remember to account for atmospheric influences and human error. It is more likely that after a steady rise, the correlation will become more and more negative, as the water bath , in which the battery sits begins to cool. Other influences, such as efficiency of the battery and the method in which it is used will also effect its performance.
Batteries conduct heat , they must have the ability to do so as they are made of metal (Zinc) and convert chemical energy into electrical, a by product of which is heat. If a battery were not built to withstand this they would over heat and become useless. As it stands they tend not to , especially not on this small scale (AA batteries) however, I do believe that the hotter the water in the bath , the more significant the change in efficiency within the battery.
As molecules in a battery obtain motion through kinetic energy (a consequence of heat energy) , the movement of the electrons within the battery slows down. Brownian motion dictate that more reaction will occur the more electrons produced (Brownian movement or motion, zigzag, irregular motion)As these reactions take place the friction within the battery will cause heat, this heat will become insulated and conducted by the water around it. This will cause internal resistance to rise also, to the point where the battery become too hot and unable to function properly. Here I cannot predict the pattern of the internal resistance but can say that the efficiency of the battery will decrease.
My battery works as follows: Being made of Magnesium oxide and Zinc both oxidisation and reduction will take place within the battery, which will effect the flow of the negative and positive ions from an anode to a cathode. The sharp increase of heat could cause thermal decomposition, altering the chemical properties of the battery and altering the mechanics of its properties. I believe that internal resistance can only increase to a certain extent before falling slightly, due the increased efficiency of the electrons moving around.
As the bag is submerged completely in water, you must make sure the thermometer is touching the part of he bag that also touches the battery, and that it is not leaking. This will nullify your results and prove a health and safety hazard.
I took readings at different intervals of current by manipulating the readings provided via the voltmeter.
It is important to respect the sensitivity of the apparatus, and any slight change in variable may completely change our results. So , I will carry out the experiment in a room where hopefully no temperature fluctuations will effect it as there are no windows or radiators, allow only one person to touch the apparatus and when recording take reading of up to four decimal places .If this proves difficult I will round up to two but bare in mind I am loosing some sensitivity of data.
You must try and keep the temperature of the water as constant as possible and counteract any cooling effects that your may see taking place. Reinforcing the insulators around that bag or continually adding boiling water can do this. However I am aware that this causes a fluctuation in temperature and may effect my results or the properties of the battery. Also this increases the chance of spilling water. I handled the batteries with tongs and wearing gloves at all times as I had previously spilt the water without realising, into the bag containing the battery, and was aware of the problems this can cause.
IT would limit me results to wait until the water reaches a required temperature. You must take whatever reading that it gives you the moment it hits the water bath. This proved awkward as my inaugural reading was the clumsy number of 78 degrees, however, I followed this trend.
Although I did everything to ensure my results were free of bias, my experiment was carried out close to a window which had the hampering effect of cooling the water (this was because it was close to a power point and sink, meaning I did not have to carry boiling water across a class room) and despite limitations of equipment, I tried to make sure all my apparatus was used to its optimum accuracy. Thermometers to +/- o.5 degrees, and the voltmeter and ammeter had readings to three decimal places.
This graph draws the conclusion that internal resistance increases with temperature up to an optimum temperature of 48 degrees. After this point , my graph depicts a gradual decline in internal resistance. I can only explain this by assuming it is not until this temperature that the electrons within the battery gain enough (kinetic) energy to create all the chemical reactions needed for better performance. It is not until here that internal resistance begins to fall.
To go further and investigate this I repeated the experiment and only added the water once it reached 40 degrees and used the kettle as a water bath which I continued to boil so the water was constantly at 100 degrees once it reached. The results proved that an optimum temperature must be obtained for internal resistance to continue to increase. My graph showed a gradual decline then a constant once it hit around fifty degrees.
I have some abnormalities on my first graph. 28 and 68 degrees. These are so obscure that they almost do not fit in the curvature, even when I have included the erroneous bars. I can only account for this with human error or unforeseeable equipment problems. Anything thing from a gust of wind, to not stirring the newly added hot water, meaning it only reheated one specific part of the bath and the other continued to cool rapidly. When I repeated my experiment (above) I deliberately placed the thermometer closer to the element in the kettle, so that the heat source was having a more direct effect. It became evident that I would get a more liner graph from this, as when the thermometer was placed in a bag it depended on good conduction from the heat source to be given a increase in temperature, when leaves gaps in my experiment, vulnerable to other variables interfering with my results.
I did not expect the resistance to be has high as it was, the physical exaggeration on the graph is due to the fact that my initial reading was 0.08 amps. A much lower current reading than I expected, this theme of providing surprising results continues and the data at 68 degrees and its inconsistency with other results can be accounted for by the same reasons. Perhaps the water was too hot, perhaps the thermometer wasn’t correct, and perhaps I left it too long. Etc, I did take measures to ensure none of the variables effected my results but due to human error , these precautionary measures were not infallible.
Some other qualitative limitations of my experiments, and so my data are : the fact I did not having a thermostatically heated water bath, the fluctuations in the temperature, which I mentioned earlier, will account for some anomalies, and the conclusion I have draw are based upon my graphs and tables of data, both of which I have not varied or been able to explore to a precisely as I would have liked and so my conclusion may be influenced by this. For instance my lines of best fit are what I have elaborated upon when concluding, however I have only drawn one type of graph.
Although these results support my hypothesis, I feel them inconclusive and unreliable and would rather redo them before taking my results any further. However how ever inconsistent the results, the defiantly prove that temper has a direct effect on internal resistance.
My results were conclusive, but did not reinforce my hypothesis consistently enough to verify my experiment. However they did obviously show that temperature has an overriding effect on internal resistance. A general trend did emerge, but I myself can account for too much error within the experiment for me to be satisfied with the results. The more readings I took the more inaccurate my data, and so I would try and keep more variables more stringently constant if I were to do this again, but also accept that in a class room of limited control atmospherically, i.e. although I tried my best ( and reasonably unsuccessfully) to maintain the temperature in the water bath, I had no control over the atmospheric temperature which surrounded the bath. Weather and central heating were the greater power here. My results will always have some discrepancies in trend.
It scientifically makes sense to assume that: As heat is induced around the battery it excites the electrons within it, providing kinetic energy to them and allowing more reactions to take place, more electrons flowing freely and through the anode and cathode and electrolyte, increasing the productivity of the battery. As more electrons are produced and obtain momentum, internal resistance decreases, made evident by experiment as there is a substantial depletion in internal resistance after 48 degrees, meaning 48 degrees is the optimum temperature for operating this battery, as I feel beyond this point, the battery will over heat.