Mass spectrometer problem -- Need help

AI Thread Summary
The discussion revolves around solving a mass spectrometer problem involving a velocity selector and the calculation of the radius of ion motion. The electric field is given as 1003.9 V/m, and the magnetic fields are Bin = 0.998 T and Bout = 0.807 T. The user initially applies incorrect formulas, leading to an incorrect velocity calculation of 12030075.19 m/s and a radius of 2.48 m. Participants emphasize the need to correctly identify the forces acting on the particle, particularly the electric force due to the velocity selector's electric field. Accurate calculations are essential for determining the correct radius for the ion's motion.
Ryan Gibbons
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Homework Statement



A mass spectrometer is constructed using a velocity selector constructed using a parallel plate capacacitor in a uniform magnetic field Bin. The electric field in the selector is 1003.9 V/m and the magnetic field in that portion of the spectrometer is Bin = 0.998 T. The balanced forces only allow specific velocities through the selector.

http://misterfig.org/pluginfile.php/1936/question/questiontext/8281/18/123907/spect.jpg
The mass of the ions can be found by measuring the radius of the motion when the ions strike point P.
The magnetic field in the circular motion chamber is Bout = 0.807 T.
What is the radius (in millimeters) for an ion of mass 2.66 x 10-26 kg and a charge of +e (1.60 x 10-19 C) ?

Homework Equations


Fm=Fe
BQV=MV^2/R
VQ=MV^2/2

The Attempt at a Solution


VQ=MV^2/2
V=2Q/M= 12030075.19 m/s

BQV=MV^2/R
R=MV/BQ=2.48 m
This is not the correct solution but i cannot figure out how to find the correct one. Please help. Thanks
 
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Ryan Gibbons said:

Homework Statement



A mass spectrometer is constructed using a velocity selector constructed using a parallel plate capacacitor in a uniform magnetic field Bin. The electric field in the selector is 1003.9 V/m and the magnetic field in that portion of the spectrometer is Bin = 0.998 T. The balanced forces only allow specific velocities through the selector.

http://misterfig.org/pluginfile.php/1936/question/questiontext/8281/18/123907/spect.jpg
The mass of the ions can be found by measuring the radius of the motion when the ions strike point P.
The magnetic field in the circular motion chamber is Bout = 0.807 T.
What is the radius (in millimeters) for an ion of mass 2.66 x 10-26 kg and a charge of +e (1.60 x 10-19 C) ?

Homework Equations


Fm=Fe
BQV=MV^2/R
VQ=MV^2/2

The Attempt at a Solution


VQ=MV^2/2
V=2Q/M= 12030075.19 m/s

You apply the wrong formula. What is the electric force on the particle?
Ryan Gibbons said:
BQV=MV^2/R
R=MV/BQ=2.48 m
This is not the correct solution but i cannot figure out how to find the correct one. Please help. Thanks
 
the electric force on the particle is 1.6x10^-19 C
 
Ryan Gibbons said:
the electric force on the particle is 1.6x10^-19 C
No, it is the charge of the particle. What force acts on it due to the electric field of the velocity selector?
 

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