Question is the title.
An extra point would be, what would be different if now the capacitor and inductor were placed in parallel. Would it still be 0?
Question is the title.
An extra point would be, what would be different if now the capacitor and inductor were placed in parallel. Would it still be 0?
The statement is not true in general. If the series combination is connected to a variable voltage source, then the capacitor's stored energy will not necessarily reach 0 at the same time that the inductor's stored energy reaches its maximum.
However, let's suppose that the inductor and capacitor aren't connected to anything that takes energy away from them or puts more energy into them. Then the total amount of energy that the two components have is constant: whenever one gains energy, the other one loses energy. That means that if one component reaches an energy minimum, then the other component has to reach an energy maximum at the same time.
The same is true if the components are in parallel instead of in series.