Describe how wet and dry barometers work.
Wet Barometer:
A wet barometer, also known as a water barometer, operates based on the principle of changes in atmospheric pressure affecting the level of liquid in a glass tube. It consists of a glass tube partially filled with water that is open at the bottom and placed in a dish containing water. The open end of the tube is sealed with your finger, while the other end is submerged in the dish of water.
As the atmospheric pressure changes, it affects the pressure on the water in the dish, causing it to rise or fall. When the pressure increases, it compresses the air inside the tube, forcing some water out from around your finger and causing the level of water in the tube to drop. Conversely, when the pressure decreases, the external pressure on the water in the dish becomes less, causing the water in the tube to push up against your finger, and the level of water in the tube rises.
By measuring the change in the water level, one can determine the atmospheric pressure. With a calibrated scale alongside the tube, the height of the water column can be used to determine the corresponding pressure.
Dry Barometer:
A dry barometer, also known as a mercury barometer, operates based on the principle of changes in atmospheric pressure affecting the height of a column of mercury in a glass tube. It consists of a long glass tube, closed at one end, filled with mercury and inverted into a dish containing more mercury. The open end of the tube is submerged in the dish, and the mercury inside the tube settles at a certain level due to atmospheric pressure.
As the atmospheric pressure changes, it affects the force exerted on the mercury in the dish, causing it to rise or fall in the tube. When the pressure increases, it pushes down on the mercury in the dish, forcing more mercury up into the tube and causing the height of the mercury column to rise. Conversely, when the pressure decreases, the weight of the column of mercury in the tube becomes greater than the external pressure, causing the mercury level to drop.
The height of the mercury column in the tube indicates the atmospheric pressure. It is often measured using a scale alongside the tube, and with the help of calculations, it can be converted into the corresponding pressure value.