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 $\frac{E_1}{E_2}$ will be

• A

  $\frac{1}{10}$
• B

  $\frac{2}{5}$
• Correct answer
  C

  $\frac{5}{13}$
• D

  $\frac{5}{26}$

Hence, the correct answer is option: 'C'.