Mercury vs Aneroid Barometer
Mercury barometer and aneroid barometer are two instruments used in the pressure measurements. These two objects use different working principles and mechanisms. The aneroid barometer and mercury barometer are two of the most important devices used in the pressure measurements. These two devices are important both practically and theoretically. In this article, we are going to discuss what aneroid barometer and mercury barometer are, their working principles, the applications of mercury barometer and aneroid barometer, their similarities, and finally the difference between mercury barometer and aneroid barometer.
A mercury barometer consists of a tube, which is closed at one end, and a beaker. The tube is filled with the barometric liquid and placed upside down in a beaker, such that the tip of the open end is in the beaker, and the remaining part is placed vertically outside of the beaker. This creates a vacuum between the liquid surface and the closed end of the tube. The pressure at the liquid surface of the beaker is equal to the external pressure. This is also equal to the pressure of the immediate surface water molecules. By principle, the hydrostatic pressure at a same height is similar for any liquid. Therefore, the pressure of a point inside the tube at the same height of the external liquid surface is equal to the external pressure. Since the pressure at the top of the tube is created by a vacuum, it is zero; also, the pressure difference between the top and the bottom of the liquid column is equal to the external pressure. By equating the force created by the pressure difference, to the weight of the liquid column, an equation for the external pressure can be obtained. P = h ρ g, where h is the height of the liquid column, ρ is the density of the liquid, and g is the gravitational acceleration. Mercury is used as the liquid because of its high density. The common unit used in mercury barometer is mercury millimeter or mmHg.
The aneroid barometer consists of a flexible metal box, which is made from an alloy of copper, and beryllium. This box is known as the aneroid cell. A strong spring prevents this box from collapsing under the external pressure. Any change in the external pressure would cause this box to contract or expand. A mechanical system is installed to amplify and indicate these changes. This is displayed using a needle and a dial. Aneroid barometers can be easily calibrated. The sensitivity of the aneroid barometer can be changed by changing the cell or the amplifying system.
What is the difference between aneroid barometer and mercury barometer?
• Aneroid barometer is a solid device, which is easy to transport and take readings, whereas, the mercury barometer is very hard to transport.
• The mercury barometer can be constructed easily, but the aneroid barometer requires machinery.
• The mercury barometer is a very large and fragile apparatus while the aneroid barometer is a compact and stable device.