Capacitors in series:

When three capacitors are connected in series.  If one electron moves from the negative terminal of the cell to the right hand plate of C₃, and one electron moves from the left hand plate of C₁ to the positive terminal of the cell, one electron will move between C₁ and C₂ and between C₂ and C₃.  Thus, the total charge moved is one electron and the charge on each capacitor is one electron.  Thus:

Q_TOTAL          =  Q₁  =  Q₂  =  Q₃

          but    V         =  V₁  +  V₂  +  V₃   (Kirchoff's second law)

          also  V         =  Q/C

          Therefore           Q/C_TOTAL = Q/C₁  +  Q/C₂  +  Q/C₃                                

          Hence  

Therefore, the three single capacitors may be replaced by a single capacitor whose capacitance (C) is given by the above equation, provided its safe working voltage is of a sufficiently high value to withstand the applied voltage.