Question

One atmospheric pressure at sea level is equal to 760 cm of Hg.
A. True
B. False

Answer 1

Pressure is ratio of force to area upon which it is acting. Atmosphere contains various gases. Those gases exert pressure. That pressure is known as atmospheric pressure. There are many ways to measure the atmospheric pressure. One of the ways is using mercury as a measuring liquid and measuring the atmospheric pressure.

Complete step-by-step answer:
The basic property of any liquid in static condition is it will align its surface perpendicular to the net force. Let us take the example of a liquid in the beaker. The force acting will be its weight and it will be acting vertically downward. Now the surface will be horizontal i.e perpendicular to the net force.
If the surface is not perpendicular then the liquid will be having acceleration along the direction of force and liquid will no longer be in equilibrium.
Similarly if we consider mercury in a measuring beaker with readings, the atmosphere will exert pressure on the fluid. That pressure will be vertical pressure and at normal atmospheric conditions mercury will align itself horizontal at a certain reading.
That reading is 760 mm under normal atmospheric conditions at sea level.
That means 76 cm of Hg at mean sea level.
Hence option B is correct.

So, the correct answer is “Option B”.

Note: There is a reason why we denote the pressure at sea level as a reference. Generally the stations where we measure pressure air at some elevation from ground. Hence the air above it will be less and apply less pressure as height increases, pressure decreases. So for every 30 feet elevation from sea level we add 1 hectopascal to get pressure at sea level.