# Repulsion between permanent magnet and air core coil

• Dante Meira
In summary, this statement is true, but it would be beneficial to seek the opinion of others before making a final decision.
Dante Meira
I formulated a statement about the repulsion between a permanent magnet and an air core coil (electromagnets without a ferromagnetic or ferrimagnetic core), and I believe this statement is true, but I would like to seek the opinion of others about it:

"In a system where an electromagnet made from an air core coil (electromagnet without a ferromagnetic or ferrimagnetic core) is in repulsion against a permanent magnet, the stronger is the magnetic field of the permanent magnet the stronger will be the force of repulsion between the electromagnet and the permanent magnet, with the volts and amperes of the direct current (DC) in the electromagnet being kept the same"

Is my statement correct?

Please try to answer this without any prejudices in mind. No preconceived ideas about "what I'm trying to do here".

Replacing the permanent magnet by another permanent magnet with a stronger magnetic field will make the force of repulsion between the permanent magnet and the air core electromagnet stronger, even if the electromagnet keeps getting the same volts and amperes of direct current?

By the way, consider the coil is made from copper wire, that is a diamagnetic material.

It is a problem that is difficult to treat precisely. In the case of another permanent magnet, you need to assume the geometry of both magnets is the same. The repulsion that occurs is not only due magnetic field strength of the permanent magnet, but also the geometry of both of its poles= geometric size of the poles and relative position, along with magnetic field strength. ## \\ ## And the force is only repulsive if like poles (i.e. the pole of the solenoid, and the pole of the permanent magnet) are facing each other.

What the coil of the electromagnet is made from is immaterial. The magnetic field comes only from the current flowing. With the current and coil being constant, the variable factor is the strength of the magnet's field. The stronger the field, the greater the repulsion, assuming like poles facing each other.

See the article for more details.
https://en.wikipedia.org/wiki/Force_between_magnets

Another way to look at it is using F=BIL, ie force experienced by a current varying wire of length L in a magnetic field with flux density (B).

Here you can clearly see, more B with same current equals more force (voltage doesn't matter in this case if the system is stationary, if the wire is moving (eg electric machine) then to develop some current (I) you will need to over come the induced voltage first (ie BEMF).

berkeman said:
So after 5 years you come back to PF to still ask others to test it?

No my friend, I'm not bothering anyone asking to test anything... I have tested it myself with neodymium magnets. And my idea was correct.

But neodymium magnets are expensive toys, even more now after the supply chain shock from the pandemic. I'm just sharing with others the idea that those iron nitride permanent magnets will be great to play with this idea in the future, and test the limits of it.

Let's embrace the experimentalist spirit of Michael Faraday:

It's hard to tell in complex and extreme cases, but in a simple linear model, if all relative positions, sizes and shapes remain the same, especially the relative distribution of the spatial magnetic field generated by the permanent magnets remains unchanged. Then the electromagnetic force between the constant current air core coil and the permanent magnet will of course increase as the strength of the magnetic field generated by the permanent magnet increases.

## 1. What causes the repulsion between a permanent magnet and an air core coil?

The repulsion between a permanent magnet and an air core coil is caused by the interaction between their magnetic fields. When two magnetic fields interact, they either attract or repel each other depending on their orientation. In this case, the like poles of the magnet and coil create a repulsive force.

## 2. How does the distance between the magnet and coil affect the repulsion?

The strength of the repulsive force between a permanent magnet and an air core coil is directly proportional to the distance between them. As the distance increases, the force decreases and vice versa. This is because the magnetic field weakens as it moves further away from its source.

## 3. Can the strength of the repulsive force be controlled?

Yes, the strength of the repulsive force can be controlled by changing the properties of either the magnet or the coil. For example, using a stronger magnet or increasing the number of turns in the coil can increase the repulsive force.

## 4. How does the shape of the magnet or coil affect the repulsion?

The shape of the magnet or coil can affect the distribution and concentration of their magnetic fields, which in turn can affect the repulsive force. For example, a horseshoe magnet will have a stronger repulsive force compared to a bar magnet of the same size due to its concentrated magnetic field.

## 5. How is the repulsion between a permanent magnet and an air core coil useful in practical applications?

The repulsion between a permanent magnet and an air core coil is utilized in many practical applications such as electric motors and generators. By controlling the strength and direction of the repulsive force, these devices can convert electrical energy into mechanical work or vice versa.

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