For an at home experiment I positioned a magnetic field so it would cross a boundary from air into water. I wanted to see if it would experience refraction similar to the refraction seen in electromagnetic fields. I also positioned a laser beam next to the magnetic field experiment so a real time comparison could be made. The results show that there was no noticeable refraction in the magnetic field. Please see the attached photo. A needle is attached to a thread to showed the direction of the magnetic field. I created several different setups to check the results. The needle never changed it’s position. My question is are these findings congruent with modern physics understanding. enter image description here

Note to moderator: please resize the photo if needed. I can’t see the photo size on my device. Thanks

  • $\begingroup$ Something to keep in mind: A static magnetic field and an EM wave are two different things. $\endgroup$ – BioPhysicist Oct 15 '18 at 3:50
  • $\begingroup$ The needle appears to be at an intermediate angle. Could you confirm ? $\endgroup$ – cumfy May 6 '20 at 21:22

Since water and air have similar magnetic permeability the magnetic field $\mathbf{B}$ does not change direction at the interface. So your experimental finding is in accordance to the current knowledge about magnetic fields in matter.

In order to see a change in direction you need to experiment with materials with considerably different magnetic permeability; then the boundary condition at the discontinuity will guarantee that the tangential component of $\mathbf{B}$ is discontinuous.

  • $\begingroup$ I don't understand. Are you suggesting that the speed of light and magnetic field are different in some mediums ? $\endgroup$ – cumfy May 6 '20 at 21:16
  • $\begingroup$ It is not about speed, it is about direction. The magnetic field is solenoidal, when you enforce this condition at an interface, the result is that the normal component of the field does not change at the interface, but the tangential component does (only if the magnetic permeability changes at the interface). $\endgroup$ – nodarkside May 7 '20 at 1:02
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    $\begingroup$ @cumfy Note that the magnetic field (which is ultimately just an "arrow" at every point in space) has no speed associated to it. It is changes in the magnetic field which propagate at $c$. $\endgroup$ – J. Murray May 7 '20 at 1:19
  • $\begingroup$ Note. The answer has been edited. Refraction is a function of light speed, not direction or magnetic permeability. $\endgroup$ – cumfy May 7 '20 at 1:27
  • $\begingroup$ It seems somewhat unlikely that the field employs some change checker prior to initiating propagation. $\endgroup$ – cumfy May 7 '20 at 1:30

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