Materials:
- One small beaker (100 ml) & one large beaker (400 ml).
- One hot plate or burner and stand.
- Boiling chips and food coloring.
Procedure:
- Put about 110 ml of water in the large beaker, a few drops of food coloring and a few boiling chips.
- Heat this beaker and the water to a boil, while the small beaker is placed upside down inside the larger beaker.
- Let the water boil for at least one full minute, taking care that the small beaker does not tip over.
- Take the two beakers off the fire and let them cool to room temperature. Observe the water level in the small beaker.
Questions:
- What would happen if after the heating, we put a few drops of cold water on the small inverted beaker
- What is inside the inverted small beaker before the heating?
- What happens to the water when we boil it?
- Why does the small beaker keep bobbing up and down?
- What do the bubbles consist of?
Explanation:
When you boil water, it makes steam, kind of like the “cloud” you see when a kettle is whistling. If you put a cup upside down over the steam, the steam goes inside and pushes the air out, like blowing up a balloon. When the steam cools down, it turns back into water drops. That makes less air inside the upside-down cup. The air outside pushes harder, so it pushes water up into the cup. If you splash a little cold water on the cup, it cools the steam faster—just like when your hot cocoa cools quicker if you blow on it—so the water rushes up even more quickly.