From the equation state for an ideal gas PV = nRT,

We have $\mathrm{V}=\left(\frac{\mathrm{nR}}{{\mathrm{P}}_0}\right)\mathrm{T}\text{ or }\mathrm{V\alpha T}$

At V = V₀, we get ${\mathrm{T}}_1=\frac{{\mathrm{P}}_0{\mathrm{V}}_0}{\mathrm{nR}}$

And at V = 2V₀, we get

${\mathrm{T}}_2=\frac{2{\mathrm{P}}_0{\mathrm{V}}_0}{\mathrm{nR}}$

For the graph of P versus T the variation is a straight line normal to the pressure axis, the temperature varies from T₁ to T₂ as shown in the figure.

For the graph of V versus T, the equation $\mathrm{V}=\left(\frac{\mathrm{nR}}{{\mathrm{P}}_0}\right)\mathrm{T}$ or V = kT shows that the volume varies directly with the temperature (Charlie's law).

So, the graph is a straight line inclined to the (V – T) axes, and passes through the origin (when produced) as shown in figure.