An accelerated iron Ion moving through a mass spectrometer's field

[slybuster]

Homework Statement

A sample of two different iron ions, Fe2+ and Fe3+, are accelerated by the same potential and then sent through the uniform magnetic field of a mass spectrometer.

a) Which ion moves faster after being accelerated?
b) Which ion follows the path with the largest radius?

Homework Equations

a)
Ek = 1/2mv^2
v= sqrt|(2qV)/m|
??v= (qBr)/m??

b)
Fc= (mv^2)/r
r = sqrt|(m2V)/(qB)|

The Attempt at a Solution

a) Stated that Fe3+ had a stronger charge and a smaller (though negligibly) mass. Related this to the Ek and v= sqrt|(2qV)/m| equations in order to show that it would have a faster velocity. I think I'm alright here...

b) This is where I have trouble. My gut tells me that the Fe2+ should have the larger radius (when I picture the charge in my head it has a lower Ek and gets deflected more). However, relating the equations is confusing me as I keep getting tripped up by thinking that the larger charge of the Fe3+ ion will cause it to experience more force and thus a wider radius pushing it. Maybe I should be picturing it enter the field from over top? (i.e. (x) and not from the side -->). Also, I want to try and set up r(Fe+3)/r(Fe+2) = ?/? but can't figure out which equation to use on the right side...

Help is very much appreciated.

 

[rude man]

Equate centripetal force to the force of a moving charge in a magnetic field. What do you get?