Two capacitance each having capacitance C and breakdown voltage V joined in series.

The general formula for effective capacitance of a series combination of n capacitors is given by

The equivalent capacitance of two capacitors in series is given by

Where

C₁ is the capacitance of the first capacitor

C₂ is the capacitance of the second capacitor

On Solving for C, we get

Since, C₁=C₂=C

Putting the values of C₁ and C₂, we get

Also, Capacitors in series have same amount of charge

∴ Q₁=Q₂=Q

Therefore, potential difference across both the capacitors are also equal to V

So, the voltage across the system is the sum of voltage across each capacitor.

Therefore, the breakdown voltage of the combination =V+V⇒ 2V

Thus, the capacitance and breakdown voltage of the combination is C/2 and 2V respectively