We have an experimental setup as below, the magnetic field strength, Bq/30s, and distances (magnet distance, Geiger counter height, Geiger to magnet centre distance) have all been recorded. The energy of the particle is also known.

We are trying to calculate the radius of a charged particle in the motion of the magnetic field, in order to prove the mass of an electron using the equation $\ r=mv/qb$.

We have tried using both the formulas for kinetic energy and Einsteins $\ e=mc^2$ in order to solve the mass and radius.

Is there any way to calculate the radius or mass of an electron using this setup? And how? Assuming we can't get any more variables.


experiemnt setup

  • $\begingroup$ Some more measurements and numbers would be useful, unless you want us to simply answer yes. $\endgroup$ – Rob Aug 4 at 2:10
  • $\begingroup$ The radius isn’t that of the magnetic field. The field goes more or less straight across between the two magnets. The radius is that of the trajectory of the beta particles moving in the magnetic field. $\endgroup$ – G. Smith Aug 4 at 2:24
  • $\begingroup$ Apologies, that is what I meant. Will edit for clarity. $\endgroup$ – Recon Aug 4 at 2:58
  1. You should not be using $E=mc^2$ as the question had nothing to do with Relativity.

  2. you have experiment, then you must have some measurement as well. in you equation $qb$ has been fixed. If you want to measure $m$ you need to find a way to resolve $r$, which seemed to be indicated in the graph.

Since $v$ constant, rewrite the equation as $rqb/m=constant$, it's evidential that you need the measurement of speed $v$. Luckily, one can resolve it by using statistics.(https://en.wikipedia.org/wiki/Strontium-90) Now you have the speed(constant), you have $q$ and $b$, measure the $r$ and one can get a solution.

(Basically what's special was the $SR-90$ source, otherwise you would lack a parameter since it's a fixed experiment. Oh, please do look for relativistic effect, $0.546 MeV $ seemed to be a big number.)

  • $\begingroup$ Doesn't that still leave two unsolved variables? Specifically, r and m, as I'm not quite sure how to measure the radius without the mass. $\endgroup$ – Recon Aug 4 at 4:16

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