Correct option is B
Mercury is used in barometers because of its high density (13.6 g/cm³) and low vapor pressure. Due to its high density, a shorter column of mercury (about 76 cm) is needed to balance atmospheric pressure, whereas water, being much less dense, would require a column about 10.3 meters high.
Additionally, mercury has low vapor pressure, meaning it does not evaporate easily, ensuring accurate and stable pressure measurements over time. If water were used, its high evaporation rate and surface tension would lead to inaccuracies.
Information Booster
- Density of Mercury: 13.6 g/cm³ (much denser than water, which has 1 g/cm³).
- Mercury Column Height: 76 cm in a standard atmospheric pressure barometer.
- Water Column Height: Would need to be 10.3 meters, making it impractical.
- Low Vapor Pressure: Prevents mercury from evaporating and affecting readings.
- Non-Adhesion to Glass: Unlike water, mercury does not stick to glass, making readings clearer.
Additional Knowledge
- (a) Mercury is available in pure form – Incorrect. While mercury is available in pure form, this is not the main reason for its use in barometers.
- (b) Mercury has high density and low vapor pressure – Correct. These properties make mercury ideal for barometers.
- (c) Mercury is shining and therefore its level can be read easily – Incorrect. Although mercury is shiny, this is only an added advantage, not the primary reason.
- (d) Mercury is a good conductor of heat – Incorrect. Thermal conductivity is irrelevant to its use in barometers.
English
15 Questions
45 Marks
18 Mins
