Question

Set up an experiment to demonstrate the effect of low pressure and particulate nuclei over water vapours.

Answer 1

Experiment to demonstrate the effect of low pressure and particulate nuclei over water vapours:

Take an empty plastic bottle and put 5‒10 mL water into it. Close the bottle tightly and shake it well. Place it under the sun for 10 minutes. Now, open the bottle and allow some smoke from an incense stick to enter it. Close the bottle tightly. Now, press the bottle with your hands for a few seconds and then release it. Again press it hardly. 

Observation- When the bottle is placed in the sunlight, the water evaporates and water vapours saturate the air inside the bottle. When the bottle is pressed hard, the internal pressure becomes high and the air inside the bottle moves to a region of low pressure. The smoke particles act as nuclei to condense the water vapours into tiny droplets. When the pressure is released, the air inside the bottle becomes foggy; and when pressure is again applied, fog disappears. 
This occurs because the smoke particles of the incense stick act as nuclei for the water vapours to condense into droplets.