Electromagnetic Induction
In 1831, Michael Faraday carried out numerous experiments in his attempt to prove that electricity could be generated from magnetism. Within the course of a few weeks, the great experimentalist not only had clearly demonstrated this phenomenon, now known as electromagnetic induction, but also had developed a good conception of the processes involved. One of the experiments performed by Faraday in that important year featured a permanent magnet and a galvanometer connected to a coil of wire wound around a paper cylinder, similar to those illustrated in this tutorial.
To simulate Faraday’s experiment, click and drag the bar magnet back and forth inside of the coil. Observe that the voltmeter linked to the coil only indicates the presence of a current when the magnet is actually in motion, and that its needle deflects in one direction when the magnet is moved into the coil and in the opposite direction when it is dragged out of the coil. Also note the magnetic field lines, depicted in blue, emanating from the magnet, and how the direction of the current (indicated in black arrows) changes depending on which way the magnet is moving. As you can observe, when the north end of the magnet enters the coil, a current is induced that travels around the coil in a counterclockwise direction; when the magnet is then pulled out of the coil, the direction reverses to clockwise.
Also notice that the current produced is stronger when the magnet is moved quickly rather than gradually. Adjust the number of turns slider and move the magnet in and out of the coil again to determine the relationship between the turns of wire in the coil and the current induced in that coil. As indicated by the voltmeter, greater voltage can be induced in coils made from a larger number of turns of wire.
Use the blue flip magnet button to see how things change when the south end of the magnet, exhibiting different field lines, interacts with the coils of wire.
In this demonstration of electromagnetic induction, the mechanical energy of the moving magnet is converted into electricity, because a moving magnetic field, entering a conductor, induces current to flow in the conductor. What also happens (though not illustrated in this tutorial) is that the current that has been induced in the wire, in turn, generates another magnetic field around the wire. This field opposes the field of the moving magnet, as explained by Lenz’s Law.
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