In 1897 J J Thomson showed that when a potential difference
of about 5000 volts was applied across two plates in a glass tub containing gas
at a very low pressure of about 0.01mmHg the tub begun to glow. When the
potential difference was increased a bright green glow appeared on the glass. Thomson
was able to prove that the glow was due to some can of rays which traveled in
a straight line from the cathode.
Observation
The cathode rays would move straight to the anode passing
through the hole in it to the zinc sulfured fluorescence
They were detected at a ray A
They were deflected away from the negative electric plates
and attracted towards the positive electric plate of the second electrode when
switched on and finally landed at a point B on the screen.
It means that the particles were negatively charged. No
matter what material the cathode is made of the rays have the same mass to charged
ratio. The rays must be basic constituency of matter and were produced by all
types of matter.
An object placed in front of the anode cast a shadow at the screen.
Conclusion: Rays travel in a straight line.
Thomson identified the negative particles as
electrons. He measured the mass ratio and concluded that distinct particles
called electrons. Based on that Thomson suggested a model. The atom which is a
solid sphere of positively charged matter with negative electron stark uniformly in it, the positive occupied
most of the volume compared to the electrons and the whole atom was neutral:
The model was called the Plum Pudding g
Model of the atom. 