What Was J.J. Thomson's Cathode Ray Experiment?

By Staff WriterLast Updated Apr 10, 2020 3:47:37 AM ET

J.J. Thomson's cathode ray experiment was a set of three experiments that assisted in discovering electrons. He did this using a cathode ray tube or CRT. It is a vacuum sealed tube with a cathode and anode on one side.


J. J. Thomson built a cathode ray tube by putting two cylinders together and sending a voltage through them. The device was known as an electrometer. It was used for sending and measuring electric charges. Thomson wanted to see if he could separate the electrical charge from the rays, and he also wanted to see if the electric charges were negative or positive.

During his first experiment, he found that when the rays entered the cylinders, they released mostly negative charges. Thomson found that by bending the rays, very little electric charge was able to pass through the cylinders. He concluded that there was no way to separate the rays and that they needed to be stuck together to function properly. All attempts failed when he tried to use the bent rays.

Thomson then went on to extract all gases from the cathode ray tube to try and identify all particles in the experiment. He was unsure if the particles were gases, atoms or matter in a finer state of subdivision.

In the third experiment, Thomson wanted to find if he could determine the basic properties of the particles. By doing so, he discovered that he could measure the ratio of the mass of a particle to its electric charge. This created electrons.