I have this question, I have an aluminium plate (or any electrically conducting plate), I place two contact electrodes on its surface so a current will flow between the electrodes, I then place the plate in a static magnetic field perpendicular to the plate (see picture). My question is : Will current flow be altered (magnetoresistance ) , or will the plate move as a solid.
Yes in principle you should measure change (increase) of resistance, because Lorentz force will affect the trajectories of electrons moving with velocity induced by electric field. BUT the aluminium is metal with many electrons on Fermi surface. Thus to reach current I, you need only small drift velocity of the electrons. Therefore also effect of Lorentz force is small (the force is proportional to velocity). This is reason why people use for such measurement semiconductors and especially two dimensional electron gas. Semiconductors (doped) have smaller concentration of free charge carriers (electrons or holes) and reduction of dimension reduces also Fermi surface.
The moving electrons cause some force on the atoms, but it is very small. The weight of electrons is 3 or 4 orders of magnitude smaller than all atom, thus the effect of electron drag is negligible.
Magnetic fields acting upon any circuits can cause a change in direction of current. The motion of the plate would also depend on the direction of magnetic field and current. Its my rudimentary answer. I hope others will answer this question better.
Interesting question....
Magnetoresistance means variation of the electrical resistivity due to an external magnetic field. The correct answer for your questions highly depends on the type of metal or conductor. If it is non-magnetic material, the external field causes a very small variation in resistivity, only can be detected at low temperatures if the magnetic field is very high. It is known as Shubnikov-De Hass effects. However, if it is magnetic conductor, the story is completely different. Depending on the relative direction of the currents and the electrons, the resistivity can change drastically or slightly, either way it can be easily measured.
There are some forces applied on the conductor but of course they are extremely small such a way that the plate wont move at all. This force is known Lorentz force of course. Noted, it is the case only for a static magnetic field. If your external field is dynamic, again the story changes. For the dynamic magnetic field, your conductor faces eddy current which applied a field in opposite direction of the external field. The field induced by the eddy current is large, and it can cause the movement of the plate (I didn't like to say the movement of the plate, because if your plate is very heavy, it may not move. But, general speaking, this force is pretty large).
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Plating