Question

A mercury barometer is enclosed in a tall glass cylinder. What happens to the level of mercury if air is slowly removed from the enclosure by means of a vacuum pump?

• A. The level steadily falls
• B. The level steadily rises
• C. The level remains unchanged
• D. The level suddenly falls to zero

Answer 1

The correct option is A The level steadily falls

Since the height of mercury in tube is equal to surrounding pressure in mm of Hg, as the air is slowly removed, pressure decreases and hence the surrounding pressure. Therefore the height of mercury column falls steadily.