Why Ignore the Magnetic Field in a Mass Spectrometer?

[darksyesider]

Homework Statement

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.

Homework Equations

qE=1/2 mv^2

F = qVxB

The Attempt at a Solution

Solution attached.

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

 

[rock.freak667]

I don't understand what you mean by ignored as the field strength is used in both calculations.