Timeline for How can magnets be used to pick up pieces of metal when the force from a magnetic field does no work?
Current License: CC BY-SA 3.0
8 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Nov 4, 2018 at 21:31 | comment | added | user87745 | Although the Maxwell equations (and relativity) mixes up the magnetic and electric field in a fundamental way, there is an unambiguous distinction as to which force is doing the work! The magnetic field (whether time-dependent or not) never works on a classical charged particle by itself. As you said, it induces the electric field which in turn does the work. Unless we invoke the objects with intrinsic magnetic dipole moment (such as an electron with a quantum mechanical spin), there is no way a magnetic field can perform work by itself. | |
| Dec 9, 2013 at 23:34 | comment | added | Selene Routley | @ArtBrown I guess it's a matter of taste: I guess I'm saying that you can't really sunder electric from magnetic fields. You need it in particular to understand the $\frac{1}{2} |\mathbf{B}|^2/\mu_0$ energy density term, which becomes a bit baffling if you take "magnetic fields can't do work" too literally. Your last sentence is true, but I guess emphasizing its converse: change is a necessary but not sufficient condition to do work | |
| Dec 9, 2013 at 23:30 | history | edited | Selene Routley | CC BY-SA 3.0 |
Fixed equation
|
| Dec 9, 2013 at 6:41 | comment | added | Art Brown | Nice answer. Two comments. (1) It may be "highly misleading to say that the magnetic field cannot do work at all", but I think your answer is consistent with the following assertions for classical physics: magnetic fields don't do work, electric fields do, and changing magnetic fields produce electric fields (and vice versa). (2) Also, not every "change on a system" does work, since that's precisely what the Lorentz force doesn't do... | |
| Aug 13, 2013 at 4:15 | comment | added | Selene Routley | @BenCrowell Hopefully done now without nicking too much of your answer. | |
| Aug 13, 2013 at 4:14 | history | edited | Selene Routley | CC BY-SA 3.0 |
Changed along the lines suggested by Ben Crowell
|
| Aug 13, 2013 at 2:32 | comment | added | user4552 | I would suggest weakening the statement in the first paragraph, since it only applies to point charges. In particular, it's false for a fundamental dipole such as an electron. | |
| Aug 13, 2013 at 1:49 | history | answered | Selene Routley | CC BY-SA 3.0 |