The effect of pressure and volume at constant temperature was first studied by Robert Boyle in 1662 which is known as **Boyle’s law**.

It states that “At constant temperature, the volume of given mass of gas is inversely proportional to its pressure”.

\[\text{i.e. } V∝ \frac{1}{P}\] \[V = \frac{K}{P} \text{ [K = Proportionality Constant]}\] \[PV = K \text{ ____(i)}\] Thus, the product of pressure and volume always remains constant.

Suppose, $P_1$ and $V_1$ be the initial pressure and volume of the gas respectively. Then, \[P_1V_1 = K \text{ ____(ii)}\] Similarly, $P_2$ and $V_2$ be the final pressure and final volume of the gas respectively. Then, \[P_2V_2= K \text{ ____(iii)}\]

From equation $(ii)$ and $(iii)$, \[P_1V_1=P_2V_2\] This equation is known as the mathematical expression for Boyle’s law.

## Graphical Representation of Boyle’s Law

**1. Plotting volume against pressure**

When volume is plotted against pressure, a hyperbolic curve is obtained. It means that when pressure increases, volume decreases and vice versa.

**2. Plotting $PV$ against $P$**

When product of pressure and volume is plotted against pressure, a straight line is obtained.

**3. Plotting reciprocal of pressure against volume**

When reciprocal of pressure is plotted against volume, a straight line is obtained in which slope can be calculated.