How does a siphon work?

 How does a siphon work? 

         A siphon is a device used to transfer a liquid from one container to another. It is shaped like a bent tube with arms of unequal length.

          A rubber or plastic tube is normally used as a siphon. One end of the tube is placed in the container containing the liquid to be transferred. The liquid is sucked from the other open end, which must be at a lower than the liquid level in the first vessel. Once the liquid starts flowing out, it will continue till the levels in both the containers are the same, or the first container is empty, or tillthe liquid level in the first container goes below the siphon tube level. 

          What makes the liquid flow from one container to the other? 

          It is the air pressure which forces the liquid to flow from the first container to the second, provided the level of liquid in the first container is higher than that in the second one. Because of the difference in the lengths of the arms, a pressure difference causes the liquid to flow. Since the upper liquid is usually exposed to the atmosphere, the maximum elevation over which a water siphon will function is about 9 metres (30 feet) which is the water equivalent of atmospheric pressure.