How to calculate force of electric current on magnet

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Discussion Overview

The discussion centers on calculating the force exerted by an electric field on a permanent magnet, exploring the relationship between electric currents (both AC and DC) and magnetic fields. Participants examine the principles underlying the interaction between electric fields and magnets, particularly in the context of applications like speakers.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant notes that a moving magnetic field can induce an electric current and conversely, an electric current can move a magnet, which is fundamental to the operation of speakers.
  • Another participant clarifies that a changing electric field generates a magnetic field that exerts force on a magnet, emphasizing that it is the magnetic field, not the electric field itself, that causes the force.
  • There is a discussion about the need for specific parameters to calculate the force on the magnet, including the current's amplitude, frequency, and phase, as well as the mass and strength of the magnet.
  • Equations are proposed to relate the magnetic field to the current and to calculate the force on the magnet, including the relationship B=B(I) and F=B*q, where q represents the magnetism of the magnet.

Areas of Agreement / Disagreement

Participants generally agree on the principles of how electric fields and magnetic fields interact, but the discussion includes varying details on the calculations and parameters needed, indicating some unresolved aspects regarding the specifics of the calculations.

Contextual Notes

Participants mention the neglect of the magnetic field due to changing electric fields at frequencies below GHz unless in specific contexts like antennas, which may limit the applicability of their discussions.

Who May Find This Useful

This discussion may be useful for individuals interested in electromagnetism, electrical engineering, and applications involving electric currents and magnetic fields, such as in audio technology.

Tord
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Hello,

It is my understanding that a moving magnetic can induce an electrical current, and that conversely, and electrical current can move a magnet. I believe that this is the basis by which speakers work (changing electric field causes vibration of the magnet that generates the sound).

My question is how would one calculate the amount a permanent magnet would move when exposed to an electric field. Another way to put it, how would you calculate the force of an electric field on a permanent magnet. Would there only be a force given an AC current of would there also be a force with a DC current?

What factors would you need to know to be able to calculate this? I would assume you would need to know:

frequency (hz) and power (Amp) of the electrical current
mass of magnet
strength of magnet (what units? gauss?)

Thanks for any help one can offer.


Tord
 
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A changing electric field generates a magnetic field which exerts force on a magnet (so its not the changing electric field by itself that exerts the force but the magnetic field that is generated by the changing electric field).

But also a current (AC or DC ) generates a magnetic field.

In order to calculate the force we ll need the equation B=B(I) that relates the magnetic field to the current I (for all frequencies below Ghz we neglect the magnetic field due to changing electric field unless we are studying electromagnetic fields from antennas that radiate electromagnetic energy).

Also we ll need to know the current (amplitude, frequency and phase if possible). From the equation B=B(I) we will be able then to calculate B. The force on the magnet from the magnetic field B will be F=B*q where q is the quantity of magnetism of the magnet measured in Newton/Tesla. Mass of the magnet will come into play to equate the Force of the magnetic field as m*a, so it would B*q=m*a where m the mass of the magnet and a its acceleration.
 
Thanks for the help, that is exactly the information I was looking for. Take care,

T
 

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