Question

The normal atmospheric pressure is
$(a){\text{ 76m of Hg}} \\\ {\text{(b) 76 cm of Hg}} \\\ {\text{(c) 76 Pa}} \\\ {\text{(d) 76N}}{{\text{m}}^{ - 2}} \\\$

Answer 1

Hint: In this question use the basic definitions of atmospheric pressure, as atmospheric pressure is the one exerted by the atmosphere. As the atmosphere is composed of many gases so obviously it exerts some pressure. Use the fact that 1mm is equal to 0.1 cm. This will help approaching the problem.

Complete step-by-step answer:

Pressure: As we know pressure is a physical force exerted on an object such that the shape of the object gets deformed by applying the pressure at a very greater extent for example hydraulic press, if we apply a normal pressure such as between the palms or by fingers so the shape of the object is not deformed.

So the atmospheric pressure is the pressure which we feel on a daily basis by the surroundings of the air.

As air is the composition of nitrogen, oxygen, argon, carbon dioxide and a small amount of other gases.

So these gases apply the pressure on our body which we cannot see by the naked eyes but it is present.

It is also known as barometric pressure, the pressure within the atmosphere of the earth.
If the pressure of the atmosphere is increased so the pressure on our body is also increased which is dangerous to our health even death is possible.

The symbol of atmospheric pressure is (atm) and the S.I unit of atmospheric pressure is pascal often denoted by (Pa) it is also measured in mm of Hg.

So the atmospheric pressure present in the surrounding of the earth atmosphere is 1 atm.

Which is equal to 101325 Pa and 760 mm of Hg.
Now as we know that 1mm = 0.1 cm.
Therefore, 760 mm = 76 cm
Therefore,
1 atm = 101325 Pa = 76 cm of Hg.

So this is the required answer.

Hence option (B) is the correct answer.

Note: Mercury (Hg) is generally taken as a standard parameter for measuring pressure. Mercury is also used in barometers (a device to measure atmospheric pressure) and the main reason behind considering it as a reference is that mercury has very high density and thus the height of this measuring device remains feasible.