Why is magnet attracting to non-magnetic copper

Copper is not a magnetic metal. Therefore, copper and magnet do not exactly attract each other.

In an experiment by NightHawkInLight, very strange behaviour occurs when a large copper plate and a strong neodymium magnet were put together.

When they are put together, the magnet does not seem to want to slip off very quickly but drags across the copper plate slowly as if it is moving through a thick fluid. Interestingly, when the magnet is dropped on the plate, it slows down midair and gently floats to the surface of copper plate. This strange behaviour is caused by electricity.

When a magnetic field moves through copper and many other metals, it causes electrons to reorganize themselves and flow in a circular pattern perpendicular to the oncoming electrons. You can imagine the electrons were very happy at the place they were before the magnet tried to move them around. So, they simply resist the change by generating a temporary magnetic field of their own.

To proof this resistance is due to the flow of electricity, NightHawkInLight then replace the copper plate with copper coil in another experiment. First, ensure the coil of wire is not connected at the ends so that it does not form a complete electrical circuit. If we tried to make electrons flow around this coil they would have nowhere to go and thus there is no resistance when you drop a magnet through the center of the copper coil wire. It just falls through the coil easily without slowing down at any point. If the resistance to movement on the magnet was an inherit property of copper, nothing to do with electricity, then the magnet should slow down even with a disconnected circuit. When you connect the two ends of the copper wire, the magnet will pause as soon as it reaches the coil and takes a moment to make it all the way through. This is because electrons can now make a complete orbit around the coil in responds to the oncoming magnetic field. As the magnet’s momentum is converted to electric current, the magnet slows down. Once the coil is disconnected and then connect both ends to an LED, the experiment of dropping the magnet through the coil will show a better indication of electricity. Unfortunately, the electricity generated is received by LED so efficiently that it doesn’t slow down the magnet quite as much as when the circuits is closed directly.

In fact, the dropping of magnet through copper coil is considered a simplified model of how most of world’s electricity is generated.

While you cannot easily get electricity from the copper plates in comparison to coil, there are still electrons flowing and caused heavy resistance to a strong magnet. Because of this, the magnet can be levitated on the copper plates of a small stand that hold out of wood and acrylic glass as shown in NightHawkInLight’s experiment. Out of surface without this property, a magnet will fly right off the side as soon as you try to lift it with the second magnet. Despite the resistance to change that we have seen, magnetic fields pass through copper as if it is not even there.

Besides the generation of electricity, there are a few other practical applications for this sort of motion damping. High speed trains and even some roller coasters use a magnetic braking system set up in a way very similar to this with powerful magnets usually electromagnets elevated above a conductive surface. The magnets slow the vehicle down quickly without any surface-to-surface friction that causes damage in conventional braking system between brake pads and rotors. The magnet’s momentum is slowed by opposing magnetic fields generated by the flow of electrons in the copper.

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The above are related to two scientific principles Faraday’s law of induction and Lenz’s law. You will learn this under the topic of “Electromagnetic induction” in Physics tuition for O Level and IP.