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Magnetism and Centripetal force question

by jumpfreak
Tags: centripetal, force, magnetism
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jumpfreak
#1
Jun12-07, 11:04 PM
P: 1
1. The problem statement, all variables and given/known data

One method for determing masses of heavy ions involves timing their orbital period in a known magnetic field. What is the mass of a singly charged ion that makes 7.0 revolutions in 1.3 x 10^-3 seconds in a 4.5 x 10^-2 T field.

a) 2.1x10^-25 kg
b) 1.3x10^-24 kg
c) 6.5x10^-23 kg
a) 5.0x10^-20 kg

2. Relevant equations

I'm not sure of which equation to use. Maybe....
Fc = Fb
m4(pi^2)r/T^2 = QvB



3. The attempt at a solution

m4(pi^2)r/(1.3x10^-3s/7)^2 = Qv(4.5x10^-2)

This might be the wrong formula.
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Andrew Mason
#2
Jun12-07, 11:43 PM
Sci Advisor
HW Helper
P: 6,653
Quote Quote by jumpfreak View Post
1. The problem statement, all variables and given/known data

One method for determing masses of heavy ions involves timing their orbital period in a known magnetic field. What is the mass of a singly charged ion that makes 7.0 revolutions in 1.3 x 10^-3 seconds in a 4.5 x 10^-2 T field.

a) 2.1x10^-25 kg
b) 1.3x10^-24 kg
c) 6.5x10^-23 kg
a) 5.0x10^-20 kg

2. Relevant equations

I'm not sure of which equation to use. Maybe....
Fc = Fb
m4(pi^2)r/T^2 = QvB



3. The attempt at a solution

m4(pi^2)r/(1.3x10^-3s/7)^2 = Qv(4.5x10^-2)

This might be the wrong formula.
It is the right formula.

If [itex]mv^2/r = qvB[/itex] where [itex]v = 2\pi r/T[/itex] then:

[tex]qB = m2\pi/T[/tex]

[tex]m = qBT/2\pi[/tex]

Just plug in the numbers.

AM
jackiefrost
#3
Jun13-07, 06:09 AM
P: 137
One caution:

In the previously cited equation [tex]m = qBT/2\pi[/tex], T is the orbital period = (1.3 x 10^-3)/7 sec


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