The greenhouse effect 2

Yasmin Jayathirtha

A few months ago in this column (Teacher Plus, April 2015), I had explored the idea of modelling the greenhouse effect. The ‘earth in a bottle’ acts as a very simple model for the earth and its atmosphere. The last experiments showed the effect of dark surfaces in absorbing and emitting radiation and acted as a model for the earth absorbing visible light and re-emitting it as infrared radiation.

This experiment shows the effect of the greenhouse gases, actually the most famous one, carbon dioxide.

Apparatus
Thermometers mercury (0-100ºC) – 3
1 dm3 bottles (plastic/glass) with stoppers – 2
Pieces of lead foil (2 cm by 3 cm) – 3
Measuring cylinder 250 cm3 – 1
Fruit salt sachets – 3

green-house-effect-bottlesExperiment
Check that the three thermometers show the same reading in air. Fix the lead foil on to the thermometer bulbs. Fix two of the thermometers into the stoppers. Add about 250 cm3 of water to the bottles and fix the stoppers. Set the bottles and the ‘bare’ thermometer in sunlight. Monitor the temperature for about 15 minutes, then add the contents of one sachet of fruit salt to one of the bottles and re-stopper it immediately. Continue to monitor the temperature for about an hour.

The fruit salt reacts with the water to form carbon dioxide. One bottle now contains an atmosphere richer (by a lot) in carbon dioxide than the other one. A set of sample readings I obtained is shown below:

The author works with Centre for Learning, Bengaluru. She can be reached at yasmin.cfl@gmail.com.

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