EVS LAB 1 AIM – To investigate how the greenhouse effect operates. SAFETY PRECAUTIONS- * Do not touch the light bulb as it would be hot. * Handle all equipment carefully, especially the thermometers and the test tubes- as these can break. VARIABLES:- INDEPENDENT VARIABLES: * Time intervals between each reading DEPENDANT VARIABLES: * Temperature readings CONTROL VARIABLES:- * Distance of one bulb to another * Height of each bulb from surface APPARATUS * 2 thermometers (mercury) * 1 test tube * Clamp stand * Stopwatch METHOD * Firstly set up the apparatus as shown below Make sure the distance and the height between the thermometers are kept the same. * Switch the bulb on. At the same start your stop watch. Make sure you keep distance from the bulb as it could be hot. * After 3 minutes , check the temperature readings in both the thermometers and record it in your raw data table. * Keep doing this till you have 10-15 readings. * Turn off the bulb DATA COLLECTION Reading Number| Temperature (Thermometer with test tube )/| Temperature (Thermometer without test tube) /| 1| 25. 2| 24| 2| 25. 2| 24| 3| 25. 5| 23. 5| 4| 25. 6| 24| | 26| 24. 3| 6| 26. 3| 25| 7| 26. 8| 25. 4| 8| 26. 8| 25. 7| 9| 27. 2| 26| 10| 27. 2| 26| Analysis About 30 percent of the sunlight that beams toward Earth is deflected by the outer atmosphere and scattered back into space. The rest reaches the planet’s surface and is reflected upward again as a type of slow-moving energy called infrared radiation. Heat travels due to radiation and hetas up both the thermometers. But the one inside the testtube gets heated more consistently. This happens because there is air trapped inside the testtube which acts as a heat store.
As the air molecules get heated, they absorb the heat and then slowly give it out in all directions as well. in the cas of the thermometer which is out in the open, the molecules simply move away and do not contribute to the heating of the thermometer. However, the molecules inside the test tube absorb heat and are not free to move. The infra red radiation given out by the trapped molecules leads to higher temperature as indicated by the thermometer. The wavelength given out by the airmolecules is of a lower wavelength and is unable to escape the test tube and thus leads to warming.
Evaluation The data is consistent with what is expected. As the temperature rises due to the heating effect of the bulb, the effect is more pronounced in the test tube. The results are totally consistent and there are no abnormal values. A possible source of error could be the uneven heating effect of the bulb but that can be minimized by ensuring that the thermometers are equidistant from the bulb, at the same height, and there is no cross wind or any fan switched on in the room. As indicated by the graph above, the temperature with the test tube stays consistently higher.
Conclusion This experiment can be used to show the heating effect of trapped air. The bulb provides heat radiation like the sun and the air inside the test tube absorbs some of the heat leading to a rise in the temperature, just like in the case of the earth and the sun. the results are consistent with what is expected, and errors if any will tend to cancel each other out. The original aim of the experiment was to study how the green house effect operates, and this has been successfully accomplished.