\(\gamma = \frac{{{C_P}}}{{{C_V}}} = \frac{5}{3}\)
we know \(\Delta Q = n{C_P}\Delta T\) and \(\Delta U = n{C_V}\Delta T\)
==> \(\frac{{\Delta U}}{{\Delta Q}} = \frac{{{C_V}}}{{{C_P}}} = \frac{3}{5}\)
i.e. fraction of heat energy to increase the internal energy be \(3/5.\)