If we rub a piece of glass with a silk or woolen cloth, then the glass is positively electrified (to understand why it is positively electrified, please read this post Is-positive-and-negative-electricity-nomenclature-arbitrary .

We say that there is an electric field around the electrified glass. What is an electric field? Is it something material? Certainly not.

If the glass is not moving, then the field is also motionless. If the glass is moving, then the field is moving together with the glass. This moving field is an electric wind. This wind, of course, is immaterial, too.

If we move the glass towards one end of a piece of metal wire, then this immaterial wind propagates through the wire to its other end (if the wire is good conductive, it could be many, many kilometers long. I emphasize that there is no closed circuit here). At the other end blowing takes place(+) . If we move the glass away from the wire, then at the other end suctioning takes place (–). With a minus electrified object, let’s say a gramophone/vinyl plate rubbed with wool, the opposite happens.

The results can be summarized as follows:

If we swing the electrified object, then an alternating current takes place in the wire piece. The faster we swing the object, the greater the intensity and the frequency of the AC.