Why ignore the magnetic field?

1. The problem statement, all variables and given/known data

Consider a simple mass spectrometer. The magnitude of the electric field between the plates of the velocity selector is 2 500 V/m and the magnetic field in both the velocity selector and the deflection chamber has a magnitude of 0.035 T. Calculate the radius of the path for a singly charged ion with mass m=2.18E-26.

2. Relevant equations

qE=1/2 mv^2

F = qVxB

3. The attempt at a solution

Solution attached.

Why is the magnetic field ignored for the velocity selector portion??

Attached Images
File Type: png Screen Shot 2014-04-22 at 5.45.31 PM.png (47.1 KB)


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