Answer:
To find out the nature of cathode rays.
Explanation:
Cathode rays tubes were born from experiment to study the conductivity of electricity in gases. The arrange of the experiment was a tube of glass with some gas inside, metallic plates in the both ends of the tube, a source of voltage and an amperemeter, as it is shown in the figure attached.
A differential potential was applied between the two plates. The one connected to the negative pole has the name “cathode” and the one connected to positive pole has the name of “anode”. Measurement of the electricity that passed through the tube between the cathode and the anode was made with different samples of gasses, then it was made with the tube in vacuum, giving as surprising result a lecture of current marked in the amperemeter (even without a material medium to travel the electric current from the cathode to the anode).
Later, variations of the experiment made for the physicist William Crookes showed at that time a “radiation” coming from the cathode (which receive the name of cathode rays). He showed that under the presence of a magnetic field the cathode rays were deviated. That gave the hypothesis that the cathode rays were made of electrical negative particles.
The particles of negative charge (electrons) were confirmed from the experiments of J.J Thomson in 1897 by the use of an electric field. With cathode of different materials, Thomson made the conclusion of all materials have this negative charge particle in their composition.
