A source of potential difference $V$ is connected to the combination of two identical capacitors as shown in the figure. When key '$K$' is closed, the total energy stored across the combination is $E_{1}$. Now key '$K$' is opened and dielectric of dielectric constant 5 is introduced between the plates of the capacitors. The total energy stored across the combination is now $E_{2}$. The ratio $E_{1} / E_{2}$ will be :