# Mass spectrometer

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1. Sep 29, 2014

### camel-man

1. The problem statement, all variables and given/known data
Consider fields of 1.4e5 N/C and 2.7 T within a velocity selector. If the charge then exits and encounters a field of 1.4 T and radius of 2.4 mm within the mass spectrometer, what would be the mass to charge ratio of this ion?

2. Relevant equations
v = E/B
m = qrB/V

q = 1.6 x 10 ^-19C
r = 2.4 x 10^-3 m
B = 1.4 T

3. The attempt at a solution

I got 51851 m/s for v

and my answer came out way off when I plugged it in for m.

I have the answer but when I try to do it myself. I get the wrong answer.

Last edited by a moderator: Sep 29, 2014
2. Sep 29, 2014

### BvU

The exercise asks for m/q, not for m. What did you get ?
And what exactly do you mean when you say 'I get the wrong answer' ?

By the way: you got 5.2 x 104 m/s, not 51851 m/s : you can't achieve five digit accuracy when all you're given is two digit numbers! But v wasn't wanted.
(However, when you work out this exercise with the given numbers in the expression for m/q, you do end up to within 1 promille of m/q of a known particle.....what a coincidence!)