What is the use of a barometer? Why does it contain mercury?

 A barometer is a scientific instrument used to measure atmospheric pressure. It is typically used to predict changes in weather patterns, such as the approach of a storm or the arrival of a high-pressure system.

Mercury is commonly used in barometers because it is a dense liquid that does not evaporate easily, making it ideal for use in a sealed tube. As atmospheric pressure changes, the level of mercury in the tube rises or falls, providing a visual indication of the pressure changes. The height of the mercury column in the tube is directly proportional to the atmospheric pressure.

However, the use of mercury in barometers has been phased out due to its toxicity and environmental impact. Today, other liquids such as alcohol or water are used instead. Electronic barometers that use sensors to measure atmospheric pressure are also commonly used.