#### An LC circuit

In a circuit capacitors store energy in electric fields, inductors store energy in magnetic fields, and energy is dissipated in resistors. What happens when a circuit has only a capacitor and an inductor and no resistance? We should find that no energy is dissipated.

Consider a series circuit with a charged capacitor, an inductor, and a switch that's initially open. When the switch is closed the capacitor starts to discharge and the current increases - energy is transferred from the capacitor to the inductor. The current peaks when the capacitor is completely discharged, at which point the capacitor starts charging the opposite way. Energy is transferred back from the inductor to the capacitor.

The process continues until the system returns to its initial configuration, and the continues to cycle.

What have we seen before that behaves in a similar way?

This behaves very much like a simple harmonic motion system, such as a mass on a spring where we can neglect friction and air resistance.