or
X
u = --- (1).
H
Now if the magnetic field H is acting alone, the curvature ρ of the path of the rays between the plates can be deduced from the deflection of the luminous patch. But we have seen that
mu
H = ---- (2).
e
From equations (1) and (2), the value of u and e/m for the particle can be determined.
The velocity u is not constant, but depends upon the potential difference between the electrodes, and this in turn depends upon the pressure and nature of the residual gas in the tube.