Question

Why was a gas at low pressure taken by Thomson while conducting the cathode ray experiment?

Answer 1

1. The experiment done by J.J. Thomson was a Cathode ray tube experiment.
2. Cathode ray tube experiment:

1. Thomson took a cylindrical glass tube with two metal electrodes and it was partially evacuated (low-pressure gas). Then, he applied a high voltage of current at either end of the tube, which lead to a discharge of a ray from the negatively charged electrode (Cathode) going towards the positively charged electrode (anode).
2. The ray emitted is called a cathode ray.
3. He concluded that the ray was actually negatively charged particles.

3. Reason: Low-pressure gas is taken because low pressure means less number of gas molecules is present in the discharge tube. Thus, there would be fewer collisions between gas molecules and the electrons that are traveling towards the anode. And hence there would be less hindrance in the formation of cathode rays.