Mass Spectrometer Formula question

[a4pat]

Homework Statement

In the velocity selector region of a mass spectrometer, an electric field of
2.34 × 10^3 N/C is perpendicular to a magnetic field, B = 1.56 × 10^-2 T.
Abeam of positive ions (q = +e) then enters a region with the same B field,
but no E field. If the ions are detected at a radius of curvature of r = 1.20m,
what is the mass of the unknown ion?

Homework Equations

m=(qBB'r)/E

The Attempt at a Solution

Got the answer m=1.99x10^-26, or 12u

The question asks for the mass of the ion, it is my understanding that the formula I used solves for the mass of the atom, not an ion. I'm not sure if the question should be asking for the mass of the unknown atom or I am not using the correct formula, in which case how do I solve the mass of the ion?Thanks

 

[anathema]

for your question! You are correct in using the formula m=(qBB'r)/E to solve for the mass of the ion. The only difference is that in this formula, q represents the charge of the ion, not the charge of the atom. So in this case, q = +e, where e is the charge of a single proton. Therefore, the mass you calculated, 1.99x10^-26 kg, is the mass of the unknown ion. This can also be written as 12 u, as you mentioned. Great job!