What are two reasons why mercury rather than water is used in barometers?
The correct answer and explanation is :
Two reasons why mercury is used in barometers instead of water are:
- High Density of Mercury
- Low Vapor Pressure of Mercury
Explanation:
- High Density of Mercury
Mercury has a much higher density compared to water. The density of mercury is approximately 13.6 times greater than that of water. This high density is crucial for barometers because it allows a mercury column to be much shorter than a water column for the same atmospheric pressure. In a typical mercury barometer, the height of the mercury column is about 760 mm (76 cm), corresponding to one atmosphere of pressure. If water were used instead of mercury, the column would need to be over 10 meters high to measure the same pressure. A shorter column makes mercury more practical for creating compact and manageable barometers. - Low Vapor Pressure of Mercury
Mercury has an extremely low vapor pressure compared to water, meaning it does not evaporate easily at normal temperatures. This is an important characteristic in ensuring the accuracy of the barometer. If water were used, its relatively higher vapor pressure would lead to significant evaporation at room temperature, which could cause air bubbles in the water column, leading to inaccurate pressure readings. The low vapor pressure of mercury ensures that it remains a liquid even under the varying pressures that might occur in a barometer, maintaining a stable and reliable reading.
Both of these factors—high density and low vapor pressure—make mercury ideal for use in barometers. These properties help produce more accurate, reliable, and practical instruments for measuring atmospheric pressure. Mercury’s density allows for a manageable column height, while its low vapor pressure ensures consistency and reliability, making it a superior choice over water.