Wikipedia:Reference desk/Archives/Science/2019 December 28

= December 28 =

Expression of a force in Bohr model of atom
Why hasn't the Lorentz force been used in Bohr model of (hydrogen) atom instead of just Coulomb force producing the orbital motion? What difference would appear in calculations of the model?(Thanks!).--109.166.134.81 (talk) 00:59, 28 December 2019 (UTC)
 * So if you are modelling a moving electron, what is making the magnetic field? It could be the nucleus, as some do have a magnetic field. However the force from the magnetic field is small compared with electric field so for approximations it can be ignored. Do you want to make your life more complicated? See hyperfine structure to see how this is taken into account. Graeme Bartlett (talk) 07:32, 28 December 2019 (UTC)
 * Other things to ignore could be that the nucleus has a finite mass, that it is not a point, but has some extended shape (see Proton radius puzzle), special relativity, (see Fine structure) and the effect of the vacuum fluctuations (see Lamb shift). Graeme Bartlett (talk) 07:35, 28 December 2019 (UTC)
 * Since you appear to be the same person asking about electric potential, you will be interested to know that in this model, the electrons are always moving, and the ground state still has the electron orbiting a nucleus. If you consider that you start with an infinitely separated electron and proton, then the work involved in electron kinetic energy (making the electron move) will come from the electrostatic potential. Graeme Bartlett (talk) 07:41, 28 December 2019 (UTC)
 * Moving electrons (and the paradox that creates) is one of the main faults of the Bohr model anyways. An electron in a curved orbit is always accelerating, and any accelerating charged particle in an electric field should radiate electromagnetic energy, per the Larmor formula.  The Bohr model was a helpful stepping stone towards a more rigorous quantum mechanical model of the atom, but even at the time it was derived, its faults were apparent.  -- Jayron 32 16:37, 2 January 2020 (UTC)


 * The Lorentz force deals with force as vector quantities, while the Coulomb force deals with force as a simple scalar quantity. Which is to say, Coulomb's Law doesn't care about directionality, it doesn't even deal with electromagnetic fields; electromagnetic field theory really doesn't come into play until 100 years AFTER Coulomb (see James Clerk Maxwell).  Coulomb's law defines electromagnetic force for a simple system of only two particles without regard for the concept of the electromagnetic field.  The Bohr hydrogen atom is a two particle system, which is why Coulomb's law works fine.  If you've only got two particles, the directionality is one-dimensional (either towards or away from each other) so you can capture that with a simple sign convention, and don't need to invoke complex vector mathematics.  I'm sure you could get the same results using the Lorentz force instead, but it's not necessary to invoke the more complex math, if you get the same result anyways; for another example why you don't use the Einstein field equations to calculate the acceleration of a falling body on earth.  You could, but simple Newtonian gravity gets the same answer, so why use the harder math?  -- Jayron 32 16:29, 2 January 2020 (UTC)

Compensation method for determination of electromotive force
How does the compensation method for determining electromotive force of galvanic cell apply in electrical circuits?--109.166.134.81 (talk) 23:59, 28 December 2019 (UTC)

What is its working principle?--109.166.134.81 (talk) 00:00, 29 December 2019 (UTC)

Does it use some bridge circuit(s)?--109.166.134.81 (talk) 13:29, 30 December 2019 (UTC)
 * The Electromotive force (emf) expressed in volts of a Galvanic cell may be measured using a wire potentiometer (see ) with a Galvanometer. Measurements can be referred to known emf's of standard cells such as the Clark cell that has been supplanted by the more stable Weston cell. Keep the potentiometer setting close to balanced, i.e. zero galvanometer current, to avoid current in the standard cell that causes deviation from its Standard electrode potential, see table . Modern voltage measuring equipment may comprise amplified high-input-impedance VTVMs or FET-VMs and a superconducting Josephson voltage standard. DroneB (talk) 17:41, 30 December 2019 (UTC)