In an LC circuit, or an LC tank, the capacitor discharges in one direction through an inductor and then the inductor seems to carry energy in the form of a magnetic field , to charge the capacitor again with current in the same direction.
While it is clear to me why a magnetic field would create that energy when it is "collapsing" into current, i don't understand how is this situation possible, since it seems like the energy coming from the capacitor when it's discharging, somehow doubles itself to charge the capacitor again with the same amount of energy , in the other direction.
I am of course deliberately ignoring the resistance, and assuming it to be zero, just to isolate and understand the functionality better.
And so, there seems to be an extra energy generated by the inductor.
How is it possible for the energy to be used twice? once in the discharge and again in the charging in the other direction. where does this extra energy come from ?
Answer
The energy is not used up. It goes to the magnetic field, and when the magnetic field is at its strongest value there is no energy left in the electric field of the capacitor. But then the magnetic field starts decreasing as the capacitor charges back up because the current starts decreasing. And when the capacitor is fully charged there is no current and no magnetic field.
The whole situation is like a pendulum swinging back and forth. When all the gravitational energy is gone, the pendulum is at its lowest point and has its max kinetic energy. When the pendulum reaches the other side and the gravitational energy "charges back up" you probably recognize there is no doubling of energy because the kinetic energy is gone.
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