# How does an inductor work?

I wonder how does an inductor resist the changing magnetic field, all the information I searched said that there is no current in the moment when the inductor is connected to the battery. This is really confusing me, no current means no magnetic field, however, to generate a magnetic field that resists changes in magnetic flux, there must be a magnetic field inside the inductor at the beginning. Therefore, I think that the maximum current should flow through the inductor at the moment of switching on, then a magnetic field that resists the change is generated to offset this current. But it doesn’t seem to be the case.

Think about it this way: A magenetic field stores energy. Therefore to create a magnetic field you must deliver energy to the system somehow. In the case of an inductor, the only input to the system that can deliver this energy is the electrical power provided to the inductor ($$I\times V$$).

And if the power provided is not infinite, then the stored energy can only change at a finite rate. Therefore the magnetic field can only change at a finite rate. Therefore the current can only change at a finite rate.

to generate a magnetic field that resists changes in magnetic flux,

It's not the magnetic field that resists changes in flux. It's the simple fact that the magnetic field stores energy that ensures that the magnetic field can't change instantaneously without providing infinite power to the device.

Therefore, I think that the maximum current should flow through the inductor at the moment of switching on,

A large current through the inductor implies a large magnetic field in the core. You must consider, where did the energy come from to generate this magnetic field?

The magnetic field can only build up slowly, because you can only provide the energy to form the field at a finite rate (i.e. finite power)

• Then how does the inductor know when it is connected to the battery, what is induced inside the inductor? – steve Jun 17 at 18:50
• @steve the battery generates a potential difference across its terminals. – The Photon Jun 17 at 19:02
• Do you mean electric field? – steve Jun 17 at 19:22
• Yes because the electric field is the gradient of the potential, you can't have one without the other (in electrostatics). – The Photon Jun 17 at 19:24
• I get it. So in the moment, the inductor soon induce the electric field and generate the magnetic field, the magnetic field then generate the opposite electric field. It stores energy in the mutual induction of electric and magnetic fields. – steve Jun 17 at 19:37