/sci/ - Science & Math

[Anonymous No.11105720]

Hi guys I'm confused about Maxwell's equations, why does a steady electric current produce a magnetic field but a steady "magnetic current" doesn't? Like why is there no J-ish term in Faraday's law? I know the go-to answers like "because magnetic monopoles don't exist" but I'm not seeing the intuition there.

So the only way to create time varying electric fields is time varying magnetic fields, and the only way to do that is to put a ""steady"" current through a wire (what about non-steady currents, like what does that mean)? But I thought movement is relative? I don't get it.

[Anonymous No.11105739]

>>11105720

If magnetic monopoles existed, you would indeed get a displacement magnetic term in Faraday's law.

Steady current will not create a time varying magnetic field. It will create a static magnetic field and no corresponding electric field.

[Anonymous No.11105773]

>>11105720
Because that is not what we observe
>>11105739
You cannot have current without an E field.

[Anonymous No.11105803]

>>11105773

You'll have an electric field in the region where there is current, yes. But assuming you don't have charge building up anywhere (ideal scenario) there will be no such field observable outside your wire, which is where your measurements will happen regardless.

[Anonymous No.11105812]

>>11105803
Sure. That's more or less what I meant. There is absolutely guaranteed to be E within the wire, though.

[Anonymous No.11105841]

>>11105739
>Steady current will not create a time varying magnetic field
ok thank you so i can only generate a time varying magnetic field with a time varying electric field which i can only do with alternating current?

[Anonymous No.11107508]

bump

[Anonymous No.11107576]

>>11105720
Magnetism is a "fictitious" force similar to centrifugal force.
It looks like it is spooky in one reference frame and it looks like the electric force in another.
https://www.youtube.com/watch?v=1TKSfAkWWN0

>>11105773
>You cannot have current without an E field.
Statically charge an object then move it mechanically.

[Anonymous No.11107584]

>>11107576
>Magnetism is a "fictitious" force similar to centrifugal force.
>It looks like it is spooky in one reference frame and it looks like the electric force in another.
No, that's not true at all. F^2=B^2-E^2 (or E^2-B^2, depending on your signature) is a constant under any Lorentz transformations, which means that there is no transformation which carries you from a purely electric field to a purely magnetic field or vice-versa.

[Anonymous No.11107592]

>>11107584
https://en.wikipedia.org/wiki/Classical_electromagnetism_and_special_relativity#Deriving_magnetism_from_electrostatics
>The chosen reference frame determines if an electromagnetic phenomenon is viewed as an effect of electrostatics or magnetism.

[Anonymous No.11107603]

>>11107592
>>11107592
>>The chosen reference frame determines if an electromagnetic phenomenon is viewed as an effect of electrostatics or magnetism.
But again, if you can write an electromagnetic phenomenon as a purely electric phenomenon in a particular reference frame, then a reference frame where you can write the same phenomenon as purely magnetic doesn't exist. Not every magnetic field can be thought of as arising from an electric field.

[Anonymous No.11107608]

>>11107603
>Not every magnetic field can be thought of as arising from an electric field.
The ones that can actually exist (no monopoles) all arise from moving charges.

[Anonymous No.11107632]

>>11107608
>>Not every magnetic field can be thought of as arising from an electric field.
>The ones that can actually exist (no monopoles) all arise from moving charges.
What about magnetic field coming from spin, like the electron magnetic dipole moment?