- #1
Academic
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Hello,
I know this topic has been posted and discussed much, but I am still not satisfied and would like some thoughts.
The common phrase is 'magnetic fields can do no work' and the source of this phrase is attributed to [tex] \mathbf{F} = \mathbf{v} \times \mathbf{B} [/tex]. I think it is clear that in the case of a current the magnetic field induces an electric field which then does the work. I always assumed this was the case for permanent magnets as well, but now have some doubts. (An often touted answer is the person moving the magnets is doing the work, but that is obviously unsatisfactory since that is the case in any conservative field.)
Now Griffith's says: "Magnetic forces do no work" and he goes on to say that "...it can be a very subtle matter to figure out what agency does [do the work]"
Physics Forums member Gokul43201 often links this page in such discussions: https://www.physicsforums.com/showpost.php?p=997210&postcount=14 and he says that the magnetic field will do work on a magnetic moment and it is this force that attracts magnets to each other, or iron filings to a magnet.
So now I see contradiction between Griffiths and
[tex]\mathbf{F} = \mu \left( \frac{\partial \mathbf{B}}{\partial z} \right) [/tex].
Is it not correct to say that this inhomogeneous magnetic field creates an electric field which does the work? And if so, then Griffith's is plainly wrong, no?
Thx for your insight!
I know this topic has been posted and discussed much, but I am still not satisfied and would like some thoughts.
The common phrase is 'magnetic fields can do no work' and the source of this phrase is attributed to [tex] \mathbf{F} = \mathbf{v} \times \mathbf{B} [/tex]. I think it is clear that in the case of a current the magnetic field induces an electric field which then does the work. I always assumed this was the case for permanent magnets as well, but now have some doubts. (An often touted answer is the person moving the magnets is doing the work, but that is obviously unsatisfactory since that is the case in any conservative field.)
Now Griffith's says: "Magnetic forces do no work" and he goes on to say that "...it can be a very subtle matter to figure out what agency does [do the work]"
Physics Forums member Gokul43201 often links this page in such discussions: https://www.physicsforums.com/showpost.php?p=997210&postcount=14 and he says that the magnetic field will do work on a magnetic moment and it is this force that attracts magnets to each other, or iron filings to a magnet.
So now I see contradiction between Griffiths and
[tex]\mathbf{F} = \mu \left( \frac{\partial \mathbf{B}}{\partial z} \right) [/tex].
Is it not correct to say that this inhomogeneous magnetic field creates an electric field which does the work? And if so, then Griffith's is plainly wrong, no?
Thx for your insight!