HALP! Mass Spec radius of circle

[Thoroughbred_Med]

Howdy,

Going over my understanding of mass specs and watching KA video (https://www.khanacademy.org/test-prep/mcat/physical-processes/atomic-nucleus/v/mass-spectrometer) I cannot understand the difference between these two formulas for the radius of the circle for an ion in mass spec:

One formula derived by setting the B=qVB equal to Fc=mv2/r is radius equals: r=mv/qB

The other formula comes from substituting the velocity of an ion in mass spec (v=sqrt(2qV/m)) into the above equation r=mv/qB and you get the radius of the ion to be: r=sqrt(2mV/qB2)

Do these equations result in the same solution for radius? Is the only difference between the equations the use of potential difference (V) in the last equation?

Thanks.

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[aldol16]

The other formula comes from substituting the velocity of an ion in mass spec (v=sqrt(2qV/m)) into the above equation r=mv/qB and you get the radius of the ion to be: r=sqrt(2mV/qB2)

They will give you the same result. The second one is perhaps more useful because you don't need to know the velocity of the particle to calculate the radius - only the applied potential difference.

 

[Thoroughbred_Med]

They will give you the same result. The second one is perhaps more useful because you don't need to know the velocity of the particle to calculate the radius - only the applied potential difference.

excellent. Thanks for the response. I thought this was the case.