Variables
- Temperature of the water boiled from the kettle
- Room temperature in which the experiment is performed
- Distance at which the thermometer as kept in the water of the container
- Distance between the person performing the experiment and the cans
Controlled variables
- Number of cans
- Amount of water
- Emissivity of cans
Independent variables
- External surface of cans
- Surface area of cans in which the water will occupy the area
Controlling Variables
Temperature of the water – The water in this experiment was used to boil from a simple kitchen kettle and hence there would be difference in the temperature. A simple way to control the variable would be by boiling the water to a higher temperature and then letting it cool down to a certain level from which the temperatures can be recorded for all the other observations to.
Room temperature- for this variable we must always check the room temperature after regular intervals. If one is performing an experiment under an AC , then the person must set the temperature at which he or she is comfortable at to carry out the whole experiment at one temperature which will be constant throughout.
Distance of the thermometer- The thermometer should be ideally be placed in the center of the water. If the thermometer is placed at either the sides of the container, this will result in an error in the reading as the outer surface of the can is affected by external temperatures.
Quantitative Data
Table show the reading taken from the shining aluminum can at equal intervals of time
Table show the reading taken from the black aluminum can at equal intervals of time
Calculation
Table below shows the mean values for the 5 observations taken for the black aluminum can in equal intervals of 20 seconds
Table below shows the mean values for the 5 observations taken for the shiny aluminum can in equal intervals of 20 seconds
Energy emitted per second can be calculated by the following formula
Energy emitted by the black can
Since we don’t know the surface area of the cans, let’s assume it to be 1 m^2.
T = temperature
Let’s take the value of the temperature as the Final reading of their temperatures at 180 seconds.
e = emissivity
σ = Stefan-Boltzmann constant
= 1x1x5.67x10^-8x352.78^4
= 878.211 W
Energy emitted by the shining can
Energy emitted by the black can
Since we don’t know the surface area of the cans , let’s assume it to be 1 m^2.
T = temperature
Let’s take the value of the temperature as the Final reading of their temperatures at 180 seconds.
e = emissivity
σ = Stefan-Boltzmann constant
= 1x1x5.67x10^-8x352.1
= 871.45 W
Conclusion
This experiment was performed to find out the effect of emissivity on the amount of energy emitted by a body. This concept revolves around black body radiation. Our assumption in the hypothesis has been proven correct. The black body after an interval of 180 seconds emits 6.761 W (approx.) more than the shining body. However the amount of energy difference that is produced is 0.7% which is very small after 180 seconds. Ideally the experiment should have been completed to about 0 degrees Celsius, but that is not possible since the average room temperature is 20 degrees Celsius and hence it will prevent the cooling of the can to 0 degree Celsius.
Evaluation
- There were many people in the lab performing the experiment. This would have let to an external influence on the regular cooling of the cylinder and hence would have prolonged the cooling leading to an error in the reading.
- The black can that was used had was actually a shining can wrap around in black paper. This wrapping if it had space between the cylinder the air between the paper between the paper and the can would get heated and hence then act as an insulator preventing the heat to escape and causing errors in the reading. An ideal improvement for this would be wrap the paper around the can securely or to just the paint the container so that there is no air stuck that would act as insulator preventing the heat to escape.
- For a lab experiment a mercury thermometer is not advisable. There are two types of mercury thermometer, partial and complete immersion. It is difficult to tell the type of thermometer. Hence if the thermometer was not dipped completely or was dipped partially it could have also caused an error. Also mercury thermometers are known to have a sensitive nod somewhere in the thermometer, which might exaggerate the reading. An ideal improvement for this would be to use digital scientific laboratory thermometer as they are more accurate and less susceptible to inaccuracies.
by
crysisfreak69yahoocom (student)
