Electromagnetic Energy: Learn the Basics

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    Electromagnet Energy
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Discussion Overview

The discussion revolves around the energy dynamics of electromagnets, particularly in relation to lifting ferrous masses against gravity. Participants explore the relationship between electric energy, force, and movement, as well as the implications of induced currents in various scenarios.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the electric energy required to hold a ferrous mass is equivalent to the energy needed without a load.
  • Another participant asserts that the energy needed to hold a suspended mass is zero since there is no movement involved.
  • A follow-up inquiry suggests that if a magnet lifts an object from the ground, there would be an increase in current due to work being done during acceleration.
  • Another participant discusses the concept of energy stored in the magnetic field and how adding a piece of iron alters the magnetic field, potentially balancing energy changes.
  • It is noted that as a conductor approaches a magnet, an induced current occurs, although there is caution about discussing "energy of magnets" due to associations with free-energy claims.
  • A later reply indicates that typically, there would be a current decrease when lifting an object, referencing the effects observed in MRI machines when external movements affect magnetic fields.

Areas of Agreement / Disagreement

Participants express differing views on the energy dynamics involved in lifting objects with electromagnets, particularly regarding whether energy is required to maintain a magnetic hold and the behavior of induced currents. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants reference concepts such as energy density in magnetic fields and the implications of induced currents, but there are no consensus definitions or resolutions regarding the energy dynamics discussed.

Who May Find This Useful

This discussion may be of interest to those studying electromagnetism, electrical engineering, or related fields, particularly in understanding the nuances of energy interactions in magnetic systems.

Austin0
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Electromagnet energy ?

Hi i have very little knowledge of electrodynamics so this is probably a no brainer but:

Given an electromagnet holding a ferrous mass suspended in gravity is the electric energy required exactly equivalent to the basis draw with no mass load??

Thanks
 
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The energy needed to do something is the applied force multiplied by the distance moved (in the direction applied). Since the suspended mass does not move... the electromagnetic energy needed to hold it there is zero.
 


Simon Bridge said:
The energy needed to do something is the applied force multiplied by the distance moved (in the direction applied). Since the suspended mass does not move... the electromagnetic energy needed to hold it there is zero.

Thanks
Does this imply that if the magnet picks something up off the ground through the air that there would be a current increase during the acceleration because work was being done?
 


Austin0 said:
Thanks
Does this imply that if the magnet picks something up off the ground through the air that there would be a current increase during the acceleration because work was being done?

If you will take a magnet and a small piece of iron,for example. Then you may put the piece of iron on a table and try to pick it up by your magnet. Eventually, you will be able to change the position of the piece by lifting in up. At first glance, it seems that you magnetic field did some work. But, there is an energy stored in the magnetic field of your magnet u = B*B/2μ. where, u - energy density, B - magnetic field , μ - magnetic permiability in μ0 units. So, If you will add a piece of iron, it will alter the total magnetic field, so increasing of the potential energy of the piece of iron will be canceled by the decreasing of the magnetic field of the system (magnet + iron).
 


As a conductor moves towards a magnet, there will be an induced current - sure.
I believe your question has been answered - you can imagine that there is some caution about answering questions about "energy of magnets" since they usually come from free-energy advocates.
 


Austin0 said:
Does this imply that if the magnet picks something up off the ground through the air that there would be a current increase during the acceleration because work was being done?
Typically it would be a current decrease, but yes. This is actually an important effect for MRI machines. Say you have a MRI scanner installed next to an elevator shaft. As the elevator comes near the magnet work is done on the elevator, the current in the coil drops, and the field is reduced. This causes visible artifacts in the images. To correct it, the MRI system has coils wound the opposite way so that as the field of one goes up the field of the other goes down.
 

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