Can gold be attracted by a magnet? If gold can be attracted to magnets, is it fake? First of all, we need to understand the working principle of magnets. Magnets can attract magnetic materials such as iron, nickel, and cobalt because the spin directions of unpaired electrons in these materials can be aligned under the action of an external magnetic field, thereby generating magnetic moments in the same direction. Eventually, the material as a whole shows magnetism.
Whether a material can have magnetism depends most crucially on the number of its unpaired electrons. Although gold is a transition metal, its electronic configuration makes it not interact with a magnetic field. The atomic number of gold is 79, and its electron configuration can be expressed as 5d106s1. In this electron configuration, the 5d orbital is already filled, and there is only one electron in the 6s orbital. The electrons in the 5d orbital all appear in pairs. The spin directions of these electrons are opposite, so any possible magnetic effects are canceled out.
Although the electron in the 6s orbital is unpaired, the magnetic moment generated by a single unpaired electron is very small and not enough to make gold show magnetism as a whole.
Gold with nanoscale size has paramagnetism
However, if the gold particles are very small, in the case of not exceeding 100 nanometers, it can be observed that gold has paramagnetism. Substances with paramagnetism will generate a weak magnetic moment in the same direction as the external magnetic field under the action of an external magnetic field, thus showing the characteristic of being attracted by the magnetic field.Then, can this principle be used to pan for gold?
In the natural environment, gold usually exists in granular or flaky forms, with sizes ranging from a few micrometers to several centimeters. In practice, it is not realistic to pan for gold using this principle. On the one hand, paramagnetic materials will be slightly magnetized under the action of an external magnetic field, but they are usually not significantly stuck to magnets. On the other hand, nanoscale gold existing in the natural environment is extremely rare, and existing technical means are difficult to effectively separate and recycle particles of such a small size.
Can gold be attracted by a magnet?If so, is it fake?
Since gold cannot be stuck by magnets, then why do news reports of gold being attracted by magnets appear? Are those golds that move along with magnets fake?
We can use copper to conduct an experiment. When a magnet passes through a thick copper tube, its magnetic field will interact with the copper tube. The copper tube can be regarded as a set of closed coils. As the magnet moves, the copper tube will cut magnetic field lines, thereby generating an induced current inside the copper tube. These induced currents will in turn generate a magnetic field opposite in direction to the magnetic field of the magnet.
Therefore, the magnet will encounter resistance opposite to its direction of motion inside the copper tube. The stronger the magnetic field of the magnet and the faster it moves, the greater the induced current generated inside the copper tube and the stronger the reverse magnetic field. This results in the phenomenon of the magnet slowly falling inside the copper tube.
Then, if we replace the copper tube with a copper plate, will the same effect be achieved?
Make a pendulum with a neodymium magnet. Place a thick copper plate on the movement path of this pendulum. When we release the magnet from a height, will it hit the copper plate?
Contrary to expectations, the violent collision between the magnet and the copper plate did not occur. When the magnet was about to approach the copper plate, its speed suddenly became very slow, and finally it gently leaned against the copper plate.
Why does the magnet stop? It is the same principle as the copper tube mentioned just now. The copper plate itself is not magnetic. As the magnet approaches, the induced current of the magnetic field lines inside the copper plate becomes stronger and stronger, and the resulting mirrored magnetic field blocks the magnet from continuing to move forward.
The faster the magnet moves, the stronger the induced magnetic field of the copper plate, and the greater the reverse thrust given to the magnet. When we throw a magnet onto a horizontal copper plate, a similar phenomenon can be observed. The magnet falls slowly at the moment before contact.
If you observe carefully, you will find that almost all videos questioning the authenticity of gold bars use neodymium-iron-boron magnets with extremely strong magnetism, and the experimenters will hang the gold bars in a bag on the edge of the table. Gold is also a good conductor. When the powerful magnetic field lines of a neodymium magnet repeatedly pass through a conductor, an induced current will be generated in it, and then a magnetic field will be produced.
In this way, when the magnet approaches, the reverse magnetic field will generate thrust on the gold bar, and when the magnet leaves quickly, the same-direction magnetic field will pull the gold bar over again.This phenomenon can create the illusion that magnets can stick to gold bars.
If a neodymium magnet is placed with a gold bar, the gold bar will not stick to the magnet. When the magnet is stationary and in contact with the gold bar, there is no changing magnetic field, so there will be no induced current generated, and the gold bar will not have any reaction. Even with a very powerful neodymium magnet, gold will not show obvious magnetic reaction.
So, the gold bar is not fake. What makes the gold bar move is the powerful magnetic field of the neodymium magnet and the induced current and eddy current drag force generated by repeated pushing and pulling.
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