Safety
Safety precautions are needed because I am dealing with hot water, which can scald. The following things need to be thought about, in order to keep this experiment safe:
- Be careful not to knock over the container with the hot water in
- Be careful not to knock over other peoples containers
- Care is needed when pouring hot water
- Do not run with the container of hot water
Diagra
Prediction
I predict that the most heat lost is in convection and evaporation.
Convection is where the cooler water particles sink down to the bottom and the warmer water particles float up to the top. If there is no lid on the beaker the warm water will float up to the top and the heat energy will escape out of the top. If a pan of water was being heated from below then the water particles at the bottom of the pan will become warm as therefore become less dense, they will begin to rise to the top of the pan. As the warmer water particles begin to rise, the cooler water particles at the top of the pan will sink to the bottom, as they are less dense. Once at the bottom of the pan, the water will start to get warmer and become less dense. This process will continue until the pan of water is at the same temperature.
Conduction is when heat energy passes through the walls of the beaker by making the particles of the beaker vibrate and then they will make the particles next to them vibrate causing the heat to pass through the walls of the beaker and out to the surroundings. Materials that are good thermal conductors tend to be good electrical conductors; metals such as gold, silver and copper have high thermal conductivity's and will conduct heat readily but materials such as cotton or rubber is a good insulator. Materials such as glass have much smaller heat transfer values and are poor heat conductors.
Conclusion
More heat was lost with evaporation and convection as the graph proves over 20 minutes by 2.5oC than conduction. A solid has molecules that are tightly packed
I was correct in my prediction.
From these statements I therefore conclude that:
- Heat loss is reduced when there is a insulator wrapped around the container
- Small pockets of air makes a excellent insulator
- The colour black is a good conductor of heat
Evaluation
I feel that I was precise when measuring volumes of water and temperature.
I measured the water with a measuring cylinder as the water meniscus just touched the line.
I also measured the temperature with a thermometer to the nearest .5 °C. I measured the starting temperature accurately.
I measured the time every minute to the nearest second with the stop clock.
I did take enough readings as I recorded the temperature once every minute for 20 minutes, which gave me 20 results
I obtained an anomalous result. This result may have been in error because I may have recorded the time at slightly different times when writing down the temperature or I miss read the temperature. To improve my experiment I would take the readings twice to make an average.
Conclusion
I concluded that the heat lost was greater by convection and evaporation than by conduction.
When the flask was covered and heat could only escape through the sides it took longer to cool as the resistance to heat lose through a conductor was greater than heat lose by convection and evaporation.
This was proved by the experiment and shows on the graph.