Materials used
- Copper
- Copper + Foil (foil shiny side in)
- Copper + Cotton Wool
- Copper + Felt
- Copper + Foil + Cotton Wool (foil shiny side in)
- Copper + Cotton Wool + Foil (foil shiny side in)
- Copper + Foil + Felt (foil shiny side in)
- Copper + Felt + Foil (foil shiny side in)
Fair Test
In order for this experiment to be fair there are certain things I must keep the same. I must keep all the same equipment e.g the kettle, thermometer and the stop clock. This is because if I used a different stopclock the timing may be slightly different to the previous stopclock used and this may affect my results.
The control is having the same volume of water each time, as well as the same start temperature. If one temperature is higher or lower then all the others then our results will be distorted because the temperature loss will be different to the others. The control also is the copper calorimeter as it doesn’t have any insulating materials on it.
- The independent variable is the material used as an insulator.
- The dependent variable is the temperature loss over a period of time.
Risk Assessment
To make sure this experiment is safe I must:
- Make sure everyone is standing up because if they were sitting down and boiling water got spilt it may go in their laps and be very painful.
- Be careful when pouring the boiling water in case it gets spilt.
Results Tables
The data that I will be collecting is the rate of temperature loss over a period of time. The first sets of results I will have are the measurements of the temperature of the water every minute. To the left is a sample table of results.
To find out the rate of energy loss I will need to find out the U-value, the surface area of the insulating jackets, temperature difference and length of time for each material. The U-value for a specified heat conductor is the heat energy lost per second through it per square meter when there is a temperature difference of 1°C between its surfaces.
To find out the surface area of the insulating jackets I need to work out the area of the lid and the area of the cylinder’s body i.e the rectangle and add together the two areas. However, the surface area needs to be in m2 so I will divide the total by 10000 to convert it from cm2 to m2 (i.e 1m2 = 100cm2 = 10000).
I will work out the temperature difference for each material after I have obtained all my results. When I have all the factors of the equation I can calculate the heat loss. The formula is:
Heat Lost = u-value x surface area x Temperature difference x Time
= J (Joules)
Results
Secondary Data – Temperature Difference
Heat Loss
The formula for heat lost is:
Heat Lost = u-value x surface area x Temperature difference x Time
Analysis
I can see from my line graph that one of my predictions was correct. Felt is the second highest point by 0.1°C. However I wasn’t correct in my prediction that Felt + Foil would be the best combination. Cotton Wool + Foil was the best combination of insulators. The worst were Copper on its own and Foil.
On the temperature difference graph you can clearly see that Copper and Foil have lost the most heat i.e the difference between their start temperature and end temperature were the greatest. You can also see that Copper + Cotton Wool and Felt have lost the least heat. This corresponds with the previous graph and as it shows that the best insulators lost the least heat and the worst insulators lost the most heat. If you refer two the second temperature difference chart you can see that those results also follow a similar pattern.
The temperature difference graph shows total heat loss due to conduction, convection and radiation whereas the heat loss ‘u-values’ graph is heat loss due to conduction only. The heat loss graph shows Foil lost the most heat energy whereas Felt lost the least. The pattern on both bar charts follows the same trend more or less. Copper and Foil are the same height on the temperature difference chart and so were Felt + Cotton Wool and Foil. However on the heat loss chart Foil is much bigger than Copper and also Cotton Wool + Foil is higher than Felt. This is because heat loss is due to conduction and so the Foil in the combination with Cotton Wool would have increased the heat loss as it is a metal and therefore a good conductor. The Foil would have increased the heat loss because it is in combination with copper (as are all others) and the two metals together make the insulator denser and consequently loose more heat through conduction.
Scientific Explanation
Felt was an effective insulator because it isn’t very dense and has lots of fibres with which to trap air with. Air is a poor conductor of heat so the more air that is trapped the less heat is conducted. These factors mean air can’t move about within the material and pass on the heat energy through convection. Cotton Wool + Foil was the best combination which was a surprise to me because I thought that Felt + Foil would be the best combination considering that Felt was the best single material at insulating. I think Cotton Wool + Foil were the best because Cotton Wool is much less dense than Felt and so was able to trap heat more effectively. The Foil would have acted as a barrier between the Cotton Wool and the air outside, seeing as it was shiny side in, thus reducing heat loss. I think the reason Felt + Foil weren't better is because of the density of Felt compared with that of Cotton Wool.
Evaluation
Validity of results
I think my experiment worked well and that my results are appropriate. They make sense and turned out to be more or less as expected. For temperature difference they are backed up by the secondary data. My results were valid because I did the experiment fairly. I used the same amount of water and same starting temperature each time. I also used the same equipment i.e copper calorimeter, kettle and thermometer. This ensured all the results were obtained the same way.
Anomalous Results
I had one set of anomalous results which were those for Foil. It lost heat far quicker than just Copper on its own which wasn’t expected. This could have been because my group was working near a window which could have been opened whilst we were doing our experiment with Foil. This would have caused a greater temperature difference between the copper calorimeter and the air temperature and speed around it. This would have caused a greater heat loss. Also, the combination of two metals could have meant there was a higher density which in turn also leads to more heat loss due to conduction.
Improving the Investigation
If I were to do this experiment again there are several things I would change or add to make it better. Firstly I could have taken two more readings which means I could then take and average reading which would cancel out any potential anomalous results. I would also use either a digital thermometer or data logging via a computer. A digital thermometer would avoid human error caused by reading off the conventional thermometer. Data logging would also avoid errors because it is done automatically. I could also test a larger range of materials/combinations.
Resources
GCSE Physics by Tom Duncan
The BBC SOS Teacher service – www.bbc.co.uk/learning/sosteacher/answers
Other various websites generated by www.google.co.uk
