Question

How is the barometric height of a simple barometer affected if

1. its tube is pushed down into the trough of mercury?
2. its tube is slightly tilted from vertical?
3. a drop of liquid is inserted inside the tube?

Answer 1

The barometric height at normal temperature and pressure:-

1. The vertical height of the mercury column from the surface of the mercury in the trough is a measure of atmospheric pressure
2. At sea level, the level of mercury in the tube is 76 cm above the level of mercury in the trough.
3. Thus, the pressure equivalent to 76 cm (or 760 mm) high column of mercury is called one atmospheric pressure, i.e.,

$1atmosphericpressure=760mmofmercurycolumn=76cmofmercurycolumn$

1. Mercury in the tube adjusts until the weight of the mercury column balances the atmospheric force exerted on the reservoir. High atmospheric pressure places more force on the reservoir, forcing mercury higher in the column. Low pressure allows the mercury to drop to a lower level in the column by lowering the force placed on the reservoir.
   When the tube is pushed down into the trough of mercury the height of the mercury column above the surface of the bottom surface remains the same.
   
2. When the tube is slightly tilted from vertical, there is no change in the height of the mercury in the tube.
   
3. If the vacuum is replaced with a drop, then the drop will exert some pressure on the mercury and there will be inaccurate readings on the barometer. The barometric height is decreased in this case. So, a vacuum is present on top of the mercury inside the tube.