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Physics Group 4 Project? ? ? ? ? ? ? ? ? ? ? After being set our initial topic of the bath tub, we chose as a group to investigate the heat lost from a bath tub. ? We initially experimented with ideas such as using different shapes, sizes and materials. ? Eventually, we decided that the easiest option was to investigate how the thickness of a bath tub effects the heat loss, as well as how conduction, convection (evaporation) and radiation effected the heat lost from a bath tub and how we could reduce these forms of heat loss. We chose to use vacuum formed plastic bath tubs as they were the quickest to build, and we did not want to waste value experimenting time building lots of bath tubs. ? The polythene plastic also mimicked the material of a real bath tub fairly successfully.
The investigation of energy (heat) lost in different bath tubs. ? ? ? ? ? ? ? ? ? ? ? We began our investigation by determining the specific heat capacity of water. In order to do this, we took a known mass of water in an insulated beaker and gave it a known quantity of energy by using an emersion heater. ? We also used an accurate thermometer in order to take the temperature change in the water. ?
We then used the equation: ? ? ? ? ? ? ? ? ? ? ? E = mc&# 8710; t We then rearranged the formula to give: ? ? ? ? ? ? ? ? ? ? ? c = E/m&# 8710; t In order to calculate the specific heat capacity of water (c), we took the known quantities of mass, energy and the change in temperature and inserted them into the above equation. In order to calculate the energy given to the water, we used electricity to heat the water, by doing this we were able to calculate the energy using P = VI. ? We measured both the voltage and the current that we used to heat the water. ? We had previously weighed the water and hence we knew the mass, and the change in temperature we measured using a thermometer. ?
Hence we were able to calculate the following values for the specific heat capacity of water: Test 1 Test 2 Test 3 Average Specific heat capacity of water 4745 4723 4216 4561? ? ? ? ? ? ? ? ? ? ? The actual specific heat capacity of water is 4200. ? We would expect our results to be lower than this value. ? However, the beaker was very well insulated with a lid and hence little heat would have been lost to the surroundings. ? The high values can be explained due to: The inaccuracy of the probe thermometer we used. ? We later found it was not the most accurate thermometer available to us. ?
For the remainder of our experiments we used a far better digital probe type thermometer. The inaccuracy of the digital ammeters, voltmeters and the unreliability of the power pack and the immersion heater. The impurities in the water which was not deionized. Background to our experiment? ? ? ? ? ? ? ? ? ? ? We researched the different methods of heat loss and came up with the following information: Conduction: The mechanism by which heat energy is transferred through solid materials.
In the case of our experiment, the heat from the water will be transferred to a certain extent through the plastic walls of the bath tub by conduction. Evaporation: The mechanism by which most energetic molecules escape from the water surface leaving the less energetic molecules behind. ? This means the internal energy of the water is then lowered and its temperature is decreased. Convection: The mechanism by which fluid? currents? , caused by the differential densities of hot and cold fluids, move. ? As the fluid gets?
hot? the particles vibrate more, and therefore expand, become less dense and rise. ? These particles then cool, become less dense and sink. For the purpose of this experiment, I will consider the heat lost by evaporation and conduction as one and the same thing as they are nearly impossible to separate in a liquid such as water. Radiation: The mechanism by which energy from the water is lost to the surroundings by electromagnetic waves. ? This occurs even at low temperatures. ?
The Investigation? ? ? ? ? ? ? ? ? ? ? We began our experiment by building two vacuum formed bath tubs of different thicknesses. ? We decided that in order to investigate the effect of thickness as well as the heat loss from conduction, convection and radiation we would undertake the following experiments. 1) We would fill both bath tubs with 700 g of water and heat them up to approximately 42. 5 degrees, the temperature of an average bath tub. ? We would then measure the heat lost from both the thick and thin bath tubs in a 45 minute period. ? We will record the change in temperature every five minutes and from this hopefully plot a heat loss curve. 2) We will then put a lid on the bath tubs to reduce the heat loss due to evaporation and repeat the same experiment. 3) We will then put insulation around the bath tubs to reduce the heat loss due to conduction and repeat the same experiment. 4) We will the paint the bath tubs silver to reduce the heat loss due to radiation and repeat the same experiment.
From these experiments we hope to be able to calculate the heat loss due to conduction, convection and radiation by virtually eliminating each of these forms of heat loss in turn and thereby calculating? how much is lost through each of these forms of heat loss. ? ? ? ? ? We wanted to make our measurements of heat loss as accurate as possible. ? After our initial experience with the inaccuracy of the probe we used for our heat capacity of water experiment we wanted to have a more accurate thermometer. We experimented with a thermocouple but the galvanometer was too sensitive for our purposes. ?
We therefore used a more accurate digital probe and calibrated it before each experiment in order to calculate the error in our readings. Experiment 1: ? ? ? ? ? In this experiment I used two vacuum formed bath tubs of differing thicknesses. Results: Time (mins) Heat Lost (C) Heat Lost (C) 5 1. 6 2. 7 10 1. 5 1. 7 15 1. 2 1. 3 20 1. 1 1. 1 25 1 1. 3 30 0. 8 0. 7 35 0. 8 0. 8 40 0. 7 0. 7 45 0. 7 0. 6 Total Heat Lost 9. 4 10. 9 I have drawn two graphs of these results to show the heat loss curve by plotting the heat lost against time for both the thick and thin bath tubs. Experiment 2: ? ? ? ? ?
In this experiment I used two vacuum formed bath tubs of differing thicknesses with lids on them. Results: Time (mins) Heat Lost (C) Heat Lost (C) 5 2 2. 3 10 1. 2 1. 2 15 1 0. 9 20 0. 8 0. 8 25 0. 7 0. 8 30 0. 6 0. 6 35 0. 6 0. 6 40 0. 6 0. 5 45 0. 5 0. 4 Total Heat Lost 8 8. 1 Experiment 3: In this experiment I used two vacuum formed bath tubs of differing thicknesses surrounded by insulation. Results: Time (mins) Heat Lost (C) Heat Lost (C) 5 1. 7 1. 9 10 1. 2 1. 3 15 1 1. 1 20 0. 9 1 25 0. 8 0. 9 30 0. 8 0. 9 35 0. 7 0. 9 40 0. 6 0. 8 45 0. 2 0. 7 Total Heat Lost 7. 9 9. 5 Experiment 4: In this experiment I used two vacuum formed bath tubs of differing thicknesses painted silver. Results: Time (mins) Heat Lost (C) Heat Lost (C) 5 2. 2 2. 3 10 1. 3 1. 5 15 1. 4 1. 4 20 1. 1 1. 3 25 1 1. 1 30 0. 8 0. 9 35 0. 8 0. 9 40 0. 8 0. 8 45 0. 5 0. 7 Total Heat Lost 9. 9 10. 9 Graph of the Total Heat Lost Conclusions to be drawn from our graph: · The lid and the surrounding insulation had a significant impact on the heat lost from the bath tub. · Painting the bath tubs silver had no real impact · The thick bath tub lost more heat than the thin one. · The silver painted bath tub lost more heat than the normal bath tub. · Heat loss was not uniform but varied. Conclusion: ? ? ? ? ? ? ? ? ? ? ? As the insulation and lid on the bath tub made a significant difference to the heat lost from the bath tub, we assumed initially that the heat lost through conduction and evaporation had been significantly reduced by the insulation and the lid respectively. ?
However, on further investigation we found that plastic is such a poor conductor that it is unlikely that any heat was lost was lost through this method and it is more likely that the heat that we initially assumed was lost through conduction was lost through radiation. ? We can therefore assume that the greatest amount of heat is lost through evaporation and some was lost through radiation, in comparison the heat lost through conduction was minute. ? The thickness of the bath tub also makes a difference, as the thicker the bath tub is, the greater the insulation, the greater the reduction of radiation. ? The silver painting did not make much difference as although some heat was reflected by it, the bath tubs were so thin that most of the heat escaped and in comparison, the heat reflected back by the silver was almost immeasurable. ? ? ? ? ? ? ? ? ? ? ? The results of our experiment showed conclusively that most of the heat was lost through evaporation, radiation also had a significant effect as when the bath was insulated the heat loss was reduced significantly. We can therefore conclude that the best bath tub would be one that was insulated and with a lid on it.
Evaluation: ? ? ? ? ? ? ? ? ? ? ? Our results were, on the whole, fairly accurate, however, we did encounter some difficulties. ? Firstly, the temperature probes we used were extremely unreliable, despite calibrating them for errors, it would take at least 30 seconds for them to settle down and reach the right temperature and therefore it is likely that during the 30 seconds the temperature would have dropped considerably and hence making our results slightly in accurate. ? In order to irradiate this, if I was to repeat the experiment I would use a computerised temperature measuring device. This would enable me to accurately plot a graph as the computer could be programmed to take the results at far more regular intervals far more accurately. ? Secondly, our methods of eliminating heat loss were not entirely reliable. ?
In each case it is likely that despite our best efforts to reduce heat loss, our insulation was not 100 % reliable. ? The worst of all our attempts to reduce heat loss was the bath tub we painted silver as the silver paint actually melted the thin bath tub making the plastic thinner and thus increasing the heat loss, hence the inconsistencies in the graph above. ? If repeating the experiment I would be careful to use thicker plastic and less silver paint. ? Furthermore, despite good results, I felt the 1 mm difference in the thickness of the two bath tubs was insufficient to give a real indication of the effect of thickness on heat loss. ? In a future experiment, I would use far thicker plastic to differentiate between the two. ? Other problems were encountered with our poor fitting insulated lids which could have been improved. ? ? ? ? ? ? ? ? ? ? ?
Despite our problems, I feel that our experiment has been a success, we worked together well as a group and our results on the whole were valid. ? Although our experiment could have been improved, and in conducting a future experiment, I would make amendments to the temperature measuring equipment particularly, through the experiment, I feel our experimental technique improved and the experience of doing a longer experiment was extremely useful.
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Research essay sample on Heat Loss Specific Heat
