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Sunday, 14 February 2016


In our previous post, we were concentrated over the various articles in relation of bearings e.g. how to understand bearing numbers. Today we will start our discussion with equation of state for a perfect gas.

Boyle’s Law

Gases have various important properties or variables such as pressure, volume, mass and temperature. These variables of gases are related with each other and magnitude of these variables or properties will determine the state of gas.

According to Robert Boyle, there will be one relationship between volume and pressure for a gas of fixed mass at constant temperature.

According to Robert Boyle, at constant temperature and for a fixed mass of gas, absolute pressure of the gas will be inversely proportional to volume of gas.

If absolute pressure of the gas is P and volume of the gas is V, at constant temperature and for a fixed mass of gas, we will have following relationship between absolute pressure P and volume V

It could also be defined as product of pressure and volume will be constant for a gas of fixed mass and constant temperature.

Above relationship is designated as Boyle’s Law as it was provided by Robert Boyle.

Let us understand Boyle’s Law with one example

Let we have a gas contained in a jar and with a provision of piston at top as shown in figure. 

Let at starting the gas has pressure 1 bar and volume 5 m3. Now we are increasing load on the top of piston for increasing the pressure while keeping temperature and mass of gas constant.

At starting, PV= 5 bar-m3

As we increase the pressure, volume of gas starts to reduce. When pressure becomes 1.5 bar, volume reduced to 3.333 m3.

At final state, PV = 5 bar-m3
PV = constant,

Robert Boyle has taken following variables as constant

  • Temperature of gas
  • Mass of the gas

Image courtesy: Google

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We will continue our discussion with another equation of state for a perfect gas i.e. Charles’s law

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