I was talking about the subject because he makes first principles about the hall effect and that question arose. Thank you, I hope you get me out of the doubt.
During Hall measurements, transient changes are not taken into consideration. Hence, under a moderate time-scale i.e., when an equilibrium of all Lorentz forces is reached, there is no need for time-measurements (of course considering time-independent uniform fields).
In the Hall effect, the measured transverse potential is in its equilibrium state, meaning that the population of accumulated charges across the sample has reached a steady state. As such, the initial non-equilibrium state is of no-relevance, even if practically measurable.
if possible, say, please, what is your material, and the exper. conditions in your Hall effect measurements[1].
1. V, I, R measurements: how to generate and measure quantities and then how to get data (resistivity, magnetoresistance, Hall) http://canfield.physics.iastate.edu/course/EM_32.pdf
Let's first consider the electron dynamics in a solid-state Hall device. In a normal magnetic field B, the normal acceleration seen by an electron due to the magnetic part of the Lorentz force is: a = eB/m.v with obvious notations. The factor eB/m is the cyclotron frequency, omega_c.
Dividing the velocity by the acceleration, one can extract a characteristic time:
tau = 1/omega_c = m/eB
One can now evaluate the characteristic time tau for a magnetic field strength spanning the range of interest for Hall measurements (since we are dealing with orders of magnitude, we can ignore here deviations due to the electron effective mass):
B= 1T tau = 6 ps
B= 1mT tau = 6 ns
B= 1µT tau = 6 µs
For electrons with effective mass smaller than 1, these times would even be smaller.
Now, these dynamic times are to be compared with other characteristic times, among others:
- The time RC for charging the output circuitry. This time depends on the sensor construction (integrated Si based Hall devices, or hybrid device Hall plate + electronics with some interconnects). It is at best in the ns range, but may be much longer ( see e.g. Crescentini et al. IEEE Trans.Instrum.Meas. 67 1470 (2018))
- The integration time necessary to smooth out the Hall sensor noise (see Mosser et al, IEEE Trans.Instr.Meas 66, 637 (2017)), in order to get a S/N ratio large enough, which depends on the magnetic field strength.
The conclusions are:
- For larger B values, the time associated with the output circuitry is larger than the dynamic time for the onset of the Hall voltage, so the active part of the Hall plate can be considered to be in steady-state, as already stated in the previous answers.
- For smaller B values, same conclusion, because realistic measurement integration times are much larger than the dynamic time evaluated above.
Now, if one would considers the Hall effect in fluids, e.g water with ions as in Hall-effect flowmeters, the ion mass M entering the Lorentz equation is much larger. I.e. for sodium ions M_Na is larger than the electron mass by a factor of 40000. Solvated ions would be even heavier. This increases a lot the dynamic times evaluated above.
However I am not familiar with that field and don't know whether it has mesurable consequences. Some help from someone working in this domain would be helpful.
Thank for your answers, You solved my doubt, although it was only a question that arose in a discussion on the hall effect.
I am currently working on the optical properties study of zinc titanate but mechanically synthesized with a high energy grinding ball sprayer. Previously I worked with mossbauer spectroscopy.
I will only add that Vincent Mosser explained quite extensively.
The time estimated by Mosser is the time during which the electron will make a complete revolution in the plane normal to the induction vector of the magnetic field, i.e. the period of rotation of the electron with cyclotron frequency (in the formula presented by Mosser omitted the factor 2p=2*3.14). This would be the case if the electron moved in a vacuum. In a solid due to the action of two forces the electron will move not in a circle but in an arc of a certain curve.
As soon as an electron in a solid with a current enters a magnetic field, the force of this field begins to act on it and deflects it from a straight trajectory. This leads to the fact that on one side of the sample accumulates a negative charge and because the sample is electro neutral on the opposite side of the sample the same uncompensated positive charge arises that leads to an electric field whose force is opposite to the magnetic field force. The more the electron deflects, the greater this force of the electric field becomes, and eventually it will be equal to the force of the magnetic field, and the deflection of the electron will stop. This time differs from the period of rotation in the presence of only one field (magnetic) t=2pm/(eB). As far as? There is something to think about.