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What is the mass of the ion

by shimizua
Tags: mass
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shimizua
#1
Mar9-09, 07:35 PM
P: 101
1. The problem statement, all variables and given/known data
A mass spectrometer applies a voltage of 2.00 kilovolts to accelerate a singly charged ion (+e). This ion then enters a region of uniform magnetic field (B= 0.400 T) which then bends the ion into a circular path of radius 0.305 m What is the mass of the ion?


2. Relevant equations
after breaking everything down from F=ma i got to m = (qB^2r^2)/2V


3. The attempt at a solution
well i am just unsure of how to find q. I know that V=2kV, B=.4 T, and r=.305 m. so if you can just help me with finding q. i can do that rest
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LowlyPion
#2
Mar9-09, 09:11 PM
HW Helper
P: 5,343
Isn't q given as +e?

http://en.wikipedia.org/wiki/Elementary_charge
shimizua
#3
Mar9-09, 09:41 PM
P: 101
ok well so i tried doing the m= -1.602x10^-19(.4^2)(.305^2)/4 and got -5.96x10^-22. would it be in kg though?

LowlyPion
#4
Mar9-09, 10:12 PM
HW Helper
P: 5,343
What is the mass of the ion

Quote Quote by shimizua View Post
ok well so i tried doing the m= -1.602x10^-19(.4^2)(.305^2)/4 and got -5.96x10^-22. would it be in kg though?
To put it in perspective for a single proton:
Quote Quote by Wikipedia
1.672621637(83)10−27 kg
drastichawk
#5
Mar9-09, 11:09 PM
P: 1
The conundrum you got going here is that the charge is +e, not e. SOO...in taking your big step in finally realizing that q is given as the charge +e, you can now go figure that the charge is POSITIVE (1.6*10^-19 C), not negative.


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