  In black hole thermodynamics, it has been observed that AdS black holes
behave as van der Waals system if one interprets the cosmological constant as a
pressure term. Also the critical exponents for the phase transition of AdS
black holes and the van der Waals systems are same. Till now this type of
analysis is done by two steps. In the first step one shows that a particular
metric allows phase transition and in the second step, using this information,
one calculates the exponents. Here, we present a different approach based on
two universal inputs (the general forms of the Smarr formula and the first law
of thermodynamics) and one assumption regarding the existence of van der Waal
like critical point for a metric. We find that the same values of the critical
exponents can be obtained by this approach. Thus we demonstrate that, though
the existence of van der Waal like phase transition depends on specific
metrics, the values of critical exponents are then fixed for that set of
metrics.
