Thermal Physics question - isulation (1 Viewer)

[selablad]

Could anyone help me with my Physics investigation? My friend and I have been working at this since Friday and haven't been able to figure it out. We've had so many problems with this experiment that I think we've just gone brain-dead or something

Anyway, this is the experiment, to investigate what sorts of materials make the best insulators and best conductors. We have a hotplate set at approximately 60 - 70 degrees with a temperature sensor to give us the exact temperature. We have a small beaker filled with honey (lower SHC than water to give us a more noticeable temp. change) and know the mass (approx. 30g). We have a temperature sensor in the honey as well.

We then record the starting temperatures of both the honey and the hotplate, and then place the insulating material and honey on the hotplate and start recording for 300 seconds with datalogger software so we get a graph over the whole time. At the end, we note the final temperature of the honey.

Our problems start when we have to do the maths. We have two equations:

Q = m c (t₂ - t₁) [1]

and

Q/t = (k (T₂ - T₁) A) / x [2]
(Fourier's Law pretty much)

The t's in [1] refer to the start and final temperatures of the honey (m and c are the mass and SHC of the honey, respectively). The t in [2] refers to the time (300s) and the T's in [2] refer to the starting temperatures of the honey and hotplate. The Q's are the same in both equations and we are using [1] to calculate Q for use in [2], the actual thermal conduction equation. k is the thermal conductivity of the particular material and what we are trying to find.

The types of materials we are using should give us values for k of round about 1, give or take a power of 10 or so. The problem is that we are getting values for k of around 0.001, even for things like aluminium which should be in the hundreds or thereabouts!

Attached is a calculation that we did for a ceramic tile, which gave a value for k of about 0.007... If anyone can help explain why we're getting such weird results, that would be greatly, greatly appreciated

 

[Forbidden.]

S.I. units?
System 'not closed' enough because the environment is interfering with the experiment?

If Thermal Physics is now in the HSC Physics syllabus woohoo!!!
lol physics deserves its own appreciation section like maths.

 

[selablad]

Thanks a lot guys. We did think that the beaker glass would affect the results, but we had absolutely no idea how else to measure it. I'm not sure where else we could put the beaker though? Unless we just got rid of the beaker completely...

Anyway, I spoke to my teacher today and she said that we were doing equation [1] wrong, and that we should consider the specific heat capacity of the material that we were using and adjust for different ones. That confused me a little as I'm not too sure of the relationship between SHC and, well, insulation. We had thought that they were pretty much the same, and that if we controlled the SHC out, then we wouldn't get different results, if that makes sense. But now I don't think that SHC and k-values have anything to do with each other, so it makes sense to put it into the equations.

What we were considering was that the honey was totally unnecessary, and that we should have a) used thicker insulating substances and b) measured the temperature directly, perhaps using a different technique. Would that improve the experiment in any major way? This isn't for the actual experiment, by the way, just suggestions and recommendations for the discussion part of my report...

Anyway, thanks for the help