An investigation into the relationship between heat loss and surface area to volume ratio

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Shehram Khattak

An investigation into the relationship between heat loss and surface area to volume ratio

Preliminary work

To investigate this relationship what I did for my preliminary work is to collect six varying volumes of water in the same boiling tube:

4cm3, 6cm3, 8cm3, 10cm3, 12cm3 and 14cm3.

The apparatus was set up as sown below.

After doing this I will then heat the boiling tube to 100°c and then start the timer, noting at every 10 second interval what the temperature is, continuing for 200 seconds altogether.  There will be a thermometer in the boiling tube telling us what the temperature of the water is and also one outside on the desk away from heat sources telling us, roughly, what the room temperature is.  

The problem which I encountered was that at this temperature the water will be boiling and ‘spitting’ hence also causing a safety hazard.  We could put anti bump granules or put some salt in it, but the salt will change the properties of the tap water, which we do not want.  However, with careful heating, the water did not get out of control.  

I noticed several mistakes with preliminary work.  Firstly I noticed that even if you are careful it is still very difficult to prevent the water from boiling violently.  Unfortunately the only measures which can be taken are to point the test tube away from your self and any other people, to boil very carefully, wear an apron and also a pair of goggles.  

Secondly I realised that the thermometer was placed free to move and that because of localised heat spots it was unable to measure the temperature properly.  What I mean by this is that some areas of the water used to be hotter than others and if the thermometer came upon that area and moved on the temperature reading would vary.  Therefore I decided to clamp the thermometer into place, thus ensuring that it doesn’t roll through heat spots.

The third thing which I noticed was the most crucial.  I gathered many results and averaged them, then checked them again but the results weren’t what I expected.  I plotted the results onto a graph.

 

As you can see the results aren’t very decisive.  My explanation was that the container in which the water was held wasn’t large enough.  I also plotted more results onto the graph, the lines were almost identical.  The reason I put forward for this is that the next volume of water was too close to that of the first.  Therefore I deduced that if I wanted to have accurate and reliable results I would have to change to a much larger container i.e. a beaker and change the volume of water I used considerably.

Planning

After taking into consideration what happened in my preliminary work I decided to fill:

A 300cm3 beaker with 300cm3 of water.

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A 125cm3 beaker with 125cm2 of water.

And a 40cm3 beaker with 40cm3 of water.

I chose these certain volumes for two reasons.  Firstly that they are far apart and so will not be similar with each other and have different gradients.

 I will have a thermometer clamped into position half way into the beaker.  I will do this because, as I learned from my preliminary work, there are localised heat spots.  So if the thermometer is clamped into a secure position these localised heat spots will not make the temperature shown on the thermometer oscillate, as the thermometer will not roll in ...

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*** A good account of differences in the rate of cooling of different volumes of water. However, the original aim has been lost sight of and the author seems unsure what the independent and dependent variables actually are.