# Energy of electric field and magnetic field

I am studying about inductors and capacitors. They store their energy in the form of electric field and magnetic field.Energy is required to create fields.But if we take an isolated charge and nothing else,electric field lines will be created .Does that take energy? I guess not .Then why does energy is stored when electric field lines are formed between the plates of the capacitor?

• Fields have real existence and not field lines. – user36790 Jun 19 '16 at 14:11

Even electrostatic fields still contain potential energy in them. The issue here is, an electron (for example) cannot interact with itself. This means that its own field cannot give it a potential energy. So yes, in the case of a lone charge completely isolated, it will create an $\vec E$ field which contains potential energy, but it will do no work until another charge is brought into the system.
Capacitors store half the work the battery does to charge it, in an $\vec E$ field. The energy stored in it is $U = \frac{1}{2}QV$. You can find out why it is half here. Basically it has to do with $I^2 R$ losses.