Long Time ago there was a man called Otto von Guerick who lived in the town of Magdeberg in Germany. One day he invited everyone in the town to come and watch a spectacular event. All the people who came to watch were very impressed with what he had done. Do you want to know what happened? He took two large copper hemispheres that fitted together. He pumped out air from in between these two hemispheres. He then tied sixteen horses, eight on each side of the hemispheres. But what was so spectacular about this? However hard they were made to pull, the horses were unable to pull the hemisphere apart! But as soon as Mr. Guerick allowed air into the sphere again, the hemispheres separated. Isn’t that wonderful?
Many of you must be wishing that if only you had horses, rope and copper hemispheres to try it out again. Well! You don’t need all these. You can repeat the Magdeberg experiment with very simple things too!
You will need: Two tins of the same size, filter paper, scissors, water, strips of paper and matchbox.
What to do:
- Take two tins of the same size.
- Estimate the diameter of the mouth of the tin.
- Cut out a circle from the filter paper that has a diameter slightly larger than the diameter of the mouth of the tins.
- Draw a circle of radius about 2cm less than the radius of the circle cut out earlier.
- Cut along the inner circle so as to make a hole.
- Wet this filter paper circle by just dipping it in water. Now place it on top of one of the tins.
- Burn a few strips of paper and drop them in the same tin.
- Quickly place the second tin on the first so that the mouths of the two tins are one above the other and the circular sheet of paper is in between the two tins.
- Now pick up the upper tin. What do you find? Does the lower tin also follow the upper one? Do they seem glued together?
The burning paper heats the air inside the tin. When air is heated, it expands and some of it escapes out of the tin. When the flame goes out, the air inside the tin cools and contracts, which takes up less space. This creates a low pressure inside the tin than outside. The greater pressure outside the tin keeps them glued.