Can the force exerted by a perm magnet be equated to electro magnet watts?

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Discussion Overview

The discussion centers around the comparison of the force exerted by permanent magnets and electromagnets, specifically whether the energy output of a permanent magnet can be equated to the energy consumption of an electromagnet in holding a weight over time. The scope includes conceptual understanding of energy, work, and the differences between permanent and electromagnets.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant proposes that a permanent magnet holding a weight for a year could be considered to output the equivalent of 87650 Watt hours, based on the energy consumption of an electromagnet holding the same weight for a shorter duration.
  • Another participant argues that a permanent magnet does not output energy in the same way an electromagnet does, as it maintains its magnetic field without energy input, unlike electromagnets which require energy due to electrical resistance and heat loss.
  • A further contribution suggests that while electromagnets consume energy, there exist more efficient designs, such as superconducting electromagnets, that could theoretically operate without energy input.
  • Another participant draws an analogy with a helicopter, indicating that while energy is used to maintain flight, a stationary object like a table can support weight without energy expenditure.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between force, work, and energy in the context of permanent and electromagnets. There is no consensus on whether the energy output of a permanent magnet can be equated to that of an electromagnet.

Contextual Notes

The discussion highlights the need for clarity in distinguishing between force and work/energy, as well as the implications of energy consumption in electromagnets versus permanent magnets.

smiddleton
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Hey guys, sorry if this is wrong place to post this. If it is let me and I will try and find the right place. It was the only category where I saw something about energy and physics. This is also probably a basic question but I hope you don't mind me asking.

Let's say you have an electro magnet that takes 10 watts to hold a 10 pound weight for 1 hour and your power supply is a 20 watt hour battery. That means it could hold that weight for 2 hours.

You also have a permanent magnet that can also hold a 10 pound weight for 1 year before its magnetic field decays and the weight drops. Does that mean that one could say that the permanent magnet is outputting the equivalent of 87650 Watt hours to hold that weight for 1 year? I came to 87650 by multiplying 10 watts by the hours in a year.
I hope that makes sense and this isn't a stupid question. Thanks in advance.
SM
 
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No, just as a table need not "output energy" to support the objects resting on it.

Electromagnets consume energy because of the electrical resistance in the wires that compose their coils. As current flows through the wires this resistance causes them to heat up, and then this heat energy is radiated away into the surroundings. The energy supplied to the electromagnet goes not into the levitated object, but into this lost heat. No work is done (no energy is transferred) by the magnetic field. It's just that this particular method of maintaining a magnetic field requires constant energy input to maintain the current in the coils.

In contrast, a permanent magnet maintains a magnetic field with no energy input at all--that's what makes it a permanent magnet. If you levitate something with a permanent magnet, no work is being done anywhere (no energy is being transferred).

The key to this is understanding the difference between force and work/energy. Work = force x distance. If you apply a constant force to something that isn't moving, no work is done.
 
As The Duck said, an electromagnet might use energy to levitate an object, but it doesn't need to. It's just an inefficient electromagnet. You could go out and get a better one, perhaps made with superconductors, and it wouldn't need any energy input at all.

Likewise, a helicopter uses energy to hover in place, but it doesn't need to. You could easily replace the spinning rotor blade and thousands horsepower engine with a table, for example. Of course you'd then be stuck in place and the helicopter would be useless, but the point remains.
 
Thanks Duck, and Lsos for the replies. They make a lot of sense. I am trying to get a good grasp on this stuff.
 

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