General > General Technical Chat
Veritasium -- How Special Relativity Makes Magnets Work.
<< < (30/47) > >>
TimFox:
arXiv physics has a similar reputation.  It is a collection of pre-prints, many of which are thereafter submitted to peer-reviewed journals.
aetherist:
It has been said (Maxwell?) that a beam of electrons in vacuo creates a surrounding magnetic field identical to that found around a current carrying wire.
However, an electron beam in vacuo does not have an associated line of protons that can be length contracted by STR.
Hence, the magnetic field around an electron beam can't have an STR explanation.
Does that falsify the STR explanation for mmf?

A single solitary lone electron flying past at speed in vacuo has they say a surrounding magnetic field.
Here, again, there is no associated line of protons. There aint even a line of electrons.
Does that falsify the STR explanation for mmf?
TimFox:
The standard explanation of this apparent discrepancy is that in Purcell's discussion of a copper wire, the wire itself is electrostatically neutral (equal positive and negative charges), so that the forces due to relative motion of the charge carriers is in addition to zero electrostatic force.
In the case of a beam of charged particles moving through vacuum, the beam is not neutral (it has a net charge), so electrostatic forces exist outside the beam.  The motion of the charged particles in the beam produces additional forces which are magnetic.
aetherist:

--- Quote from: TimFox on April 08, 2022, 12:39:59 pm ---The standard explanation of this apparent discrepancy is that in Purcell's discussion of a copper wire, the wire itself is electrostatically neutral (equal positive and negative charges), so that the forces due to relative motion of the charge carriers is in addition to zero electrostatic force.
In the case of a beam of charged particles moving through vacuum, the beam is not neutral (it has a net charge), so electrostatic forces exist outside the beam.  The motion of the charged particles in the beam produces additional forces which are magnetic.

--- End quote ---
Has anyone ever measured a wire-like magnetic field around an electron beam?
TimFox:
Yes.  There are commercial sources for vacuum-compatible search coils that can sense a pulsed beam of charged particles flowing through the hole in the coil.
Here is one commercial source with several different coil configurations built into vacuum flanges:  https://www.bergoz.com/products/
A coil senses the time-derivative of the magnetic field around the beam, dBdt, as the pulsed beam goes through it.
Here is a tutorial from Fermilab about various "beam diagnostics", including measuring the field induced by the beam current, similar to how clamp-on ammeters measure normal AC through an insulated wire.
https://lss.fnal.gov/archive/2000/conf/Conf-00-119.pdf
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod