Chainus

Meet Chainus, two capacitors holding hands in a line, who together hold less than either one alone.

A capacitor stores charge on two metal plates separated by a gap. When capacitors are joined one after another in series, the same charge must build up on every one of them, because charge that leaves one plate has to land on the next. The battery's voltage is shared between them.

The total capacitance obeys 1/C = 1/C₁ + 1/C₂. A 6 μF and a 3 μF capacitor in series give C = 2 μF, smaller than either.

On a 12 V battery the pair stores Q = CV = 24 μC. Each capacitor carries that same 24 μC, so the 6 μF one has 4 V across it and the 3 μF one has 8 V. The smaller capacitor takes the bigger share of the voltage.

Engineers chain capacitors to handle voltages that would break a single one. Put them side by side in parallel instead, and their capacitances simply add.