Question

Take two similar transparent glass bottles having wide mouths. Put a few crystals of potassium permanganate or pour a few drops of ink in one bottle. Fill this bottle with hot water. Fill the other bottle with cold water. Cover the cold water bottle with a thick piece of paper such as a postcard. Press the postcard firmly with one hand and hold the bottle with the other hand. Invert the bottle and place it on top of the hot water bottle. Hold both the bottles firmly. Ask some other person to pull the postcard. Observe what happens. Explain.
Topic: Heat

Answer 1

First bottle contains hot water and ink with KMnO4 and second bottle contains cold water and ink with KMnO4.

When second bottle is inverted on top of first bottle, the ink diffuses from the first bottle.

The reason is small particles move freely around high kinetic energy. The RMS velocity is higher than the second bottle. So the particles move from hot to cold water bottle.

Answer 2

When the card will be removed, then due to diffusion process there will be movement of colored hot water in upward direction and cold water in downward direction. It happened because hot fluid i.e. hot water is lighter than the cold water.