Predicting Heat Loss from Glass Beaker Experiment

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Homework Help Overview

The discussion revolves around an experiment designed to measure how the temperature of water in a glass beaker affects the rate of heat loss. The original poster has conducted tests and is seeking predicted results for comparison, focusing on the thermal conductivity of glass and the relevant equations.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply an equation for thermal current to calculate heat loss at various temperatures, but questions the reasonableness of their results and the conversion of watts to temperature change over time. Other participants question the accuracy of the area calculation used in the formula and suggest that the original poster may need to consider additional factors, such as the dimensions of the beaker and the volume of water it contains.

Discussion Status

Participants are actively engaging with the original poster's calculations, providing feedback on the area used in the thermal current equation and expressing concerns about the high values obtained. Some guidance has been offered regarding unit checks and the need for more accurate measurements, but there is no explicit consensus on the correct approach yet.

Contextual Notes

The original poster notes a lack of precise measurements for the beaker and is uncertain about the area calculations, which may affect the results. There is also a discussion about the relationship between watts and temperature change, indicating a need for further clarification on these concepts.

vr_ben
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Homework Statement


Alright so I am doing a fairly simple experiment testing how the temperature of water in a beaker effects how fast heat is lost. Have done the tests, but need to get some predicted results to compare them too.

Have been using a glass beaker filled with 200ml of water, beaker dimensions being 60mm diametre, 150mm tall, about 1.5mm thick (actually forgot to measure this, so if this is off let me know :P)

Thermal conductivity of glass: 0.8

The Attempt at a Solution


Ok so i used an equation for thermal current:
I = kA (Change in T/ Chane in x) with I being current (Watts) k being thermal conductivity, A being cross sectional area (i calcualted 28.27cm^2 but not sure if that's correct), T being temperature (Kelvin), x as distance current travels.

Anyway using that equation i calcualted it for a few different temperatures and got:
change in temp - Thermal current
70 - 10554.13W
60 - 9646.4W
50 - 7538.6W
40 - 6030.93W
30 - 4323.2W
20 - 3015.46W

And this is where I am sort of stuck. First of all are those reasonable numbers (seem quite high to me...)? and is there a way to convert W to degrees per second or minute or something which i could actually compare to real results?

Anyway if you read all that and can help in anyway way its much appreciated
thanks
 
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umm bump? anyone able to help, am i even using the right formula?
 
How did you get that area? It is too small.

ehild
 
oh i think that was just the area of the bottom, maybe, did this a while ago.. suppose i need to include the sides aswell? Didnt get real measurements of the beaker which is a shame... but including the side it would be something like 250cm^2?

That makes the current even higher.

Anyway thanks for that, is there a way to get a temperature per second loss or something from the answers in W? (is a watt = JS^-1?, and if so can i change that to temperature loss?)
 
Your formula for the heat loss per unit time which is Js^-1 is correct, but the results are really too high. Check the units and your calculations.
As for the area of the side of the baker that conducts heat, take into account that the 200 ml water does not fill the baker.

ehild
 

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