the apparatus is shown diagramatically in figure. the beam of +ve ions produce in discharge tube is collimated by two slits S1 and S2 and enter a "velocity sector". the velocity sector consisit of steady electric fild X maintained at right angle to the ion beam between two plain parallel plates P1 and P2 and a megentic field B. the megnetic field is produce by an electromegnet represented by a dotted circle. the megnetic field B is perpendiculer to X and the ion beam. the electric field and megnetic field of the velocity sector are so adjusted that deflection produce by one is nullified by the other. If X and B are the electric field and megnetic induction. then,
Xe=veB
v=X/B
Only those ion having the velocity v alone pass through the entry slit S3 to enter the evacuated chamber D. thus all ion entering the evacuted chamber must have sane velocity. the positive ion which enter into D are subjected to a strong unifrom megnetic field of intensity B', perpendicuar to its path. the force acting on each ion willbe Bev. Ion with different masses trace circular path of different radii given by
R = Mv/B'e {since Bev=Mv^2/r}
e/M = v/BR = X/BB'R {since v=X/B}
since v and B' are constant quantities, e/M ∝ 1/R
After describing the semicircle, the ion strike a photographic plate.
NOW, M = B'eR/v. if e is same for all ions then M ∝ R.
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