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.

Answer 1

Observation and Explanation:

1. Setup:

   • Take two similar transparent glass bottles with wide mouths.
   • Put a few crystals of potassium permanganate or a few drops of ink in one bottle and fill it 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 cold water bottle and place it on top of the hot water bottle.
   • Hold both bottles firmly and ask someone to pull the postcard.

2. Observation:

   • When the postcard is pulled out, the coloured hot water from the bottom bottle rises and mixes with the cold water in the top bottle, creating a convection current.

3. Explanation:

   • Hot water is less dense than cold water. When the postcard is removed, the hot water from the bottom bottle rises into the cold water bottle, and the cold water descends. This movement is due to the difference in density and results in the formation of a convection current, visibly mixing the colors in the water.