Final answer:
The water in the pipe does not rise above the level of the water in the cistern due to the principle of communicating vessels.
Step-by-step explanation:
When an empty pipe is placed in a cistern of water, the water in the pipe does not rise above the level of the water in the cistern due to the principle of communicating vessels. This principle states that when two or more containers are connected and filled with a fluid, the fluid level will be the same in all connected containers.
In this case, the cistern and the pipe are connected, and water flows between them until the levels in both become equal. Since the pipe is initially empty, the water level in it will rise to the same level as the cistern, maintaining equilibrium.
For example, if you connect two glasses with a straw and fill one of them with water, the water levels in both glasses will eventually be the same because the water can freely flow through the straw.
Learn more about Principle of communicating vessels