Describe the Construction and working of mecury barometer
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Answer:
All about a barometre
A barometer is an instrument that is used to measure pressure.
How do we create it ?
We can create a simple mercury barometer by filling a long tube completely with mercury. We then fill a basin completely with mercury, and upturn the tube into the basin such that no liquid spills out. Then, we will notice the mercury level drop and reach a constant.
By measuring the height of mercury above the liquid surface, we can measure pressure as P=ρgh
At atmospheric pressure, the mercury will rise to a height of 76cm
how does a bareometre work?
*Air pressure at any level in the atmosphere depends on the weight of the air overhead. A mercury barometer is basically just a scale that measures the weight of the atmosphere above.
*A barometer is essentially a balance.
The weight of the atmosphere is balanced by the weight of a much shorter mercury column.
*You can't use an ordinary pan balance to weight the atmosphere (because air is pushing down on both sides). A U-shaped tube filled with some kind of liquid that can slosh back and forth would work. Such an instrument is called a manometer and is often filled with mercury.
*To turn the manometer into a true barometer, we'll extend the tube on the right and close the top so that air isn't pushing down on the mercury. We'll also use somewhat larger cylindrical columns of air and mercury that completely fill the insides of the tube.
The weight of a very tall cylindrical column of air is balanced by a much shorter cylindrical column of mercury. The height of the mercury column will change as air pressure varies.
Mercury is a liquid. You need a liquid that can slosh back and forth in response to changes in air pressure. Mercury is also very dense which means the barometer won't need to be as tall as if you used something like water. A water barometer would need to be over 30 feet tall. With mercury you will need only a 30 inch tall column to balance the weight of the atmosphere at sea level under normal conditions (remember the 30 inches of mercury pressure units mentioned earlier). Mercury also has a low rate of evaporation so you don't have much mercury gas at the top of the right tube (there's some gas, it doesn't produce much pressure, but it would be hazardous you if you were to start to breath it).
*Here is a more conventional barometer design. The bowl of mercury is usually covered in such a way that it can sense changes in pressure but sealed to keep poisonous mercury vapor from filling a room.
I hope it helps you!!!