Question

Blowing air with an open mouth is an example of:
A) Isobaric process
B) Isochoric process
C) Isothermal process
D) Adiabatic process

Answer 1

Hint : When we open our mouth to blow air, the pressure inside and outside our mouth is the same. We will use this property to determine the kind of process blowing air out of our open mouth is.

Complete step by step answer
In the process of blowing air, let us consider our mouth as the system and our environment as the surroundings.
In an isochoric process, the volume of the system remains constant. When we blow air with an open mouth, the volume of the air occupied by the air in our lungs decreases and the volume in the atmosphere increases so it is not an isochoric process as the volume of air inside the system is not constant with time.
In an isothermal process, the temperature of the system remains constant. Blowing air causes the temperature of the air to rise by a very slight amount as the average velocity of the gas increases. So, it is not an isothermal process either.
In an adiabatic process, the heat exchange between the system and the surroundings is zero. But when we blow air, we are transferring energy in the form of blowing air so there is a transfer of heat energy between the system and the surroundings so it is not an adiabatic process either.
In an Isobaric process, the pressure of the system remains constant. When air is blown with an open mouth, its pressure is the same as that of atmospheric pressure since it is in direct contact with the atmosphere. Hence it is an isobaric process that corresponds to option (A).

Note
We must know the classification of different kinds of processes to answer such questions. The pressure inside our body is usually equal to the atmospheric pressure. Since our mouth is open when blowing air, it will have the same pressure as the atmosphere and it won’t change with time.