Given, $\left( p + \frac{a}{V^{2}} \right)(V - b) = RT$ According to principle of homogeneity Dimension of $\frac{a}{V^{2}} =$ dimension of $p$ Dimension of $a =$ dimension of $p \times$ dimension of $V^{2}$ $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = \left\lbrack ML^{- 1}T^{- 2} \right\rbrack\left\lbrack L^{3} \right\rbrack^{2} = \left\lbrack ML^{5}T^{- 2} \right\rbrack$