jj thomson cathode ray experiment summary

#JJ THOMSON CATHODE RAY EXPERIMENT SUMMARY SERIES#

Thomson came up with the initial idea for the structure of the atom, postulating that it consisted of these negatively charged particles swimming in a sea of positive charge.

He decided upon the latter and came up with the idea that the cathode rays were made of particles that emanated from within the atoms themselves, a very bold and innovative idea. Thomson found out that the charge to mass ratio was so large that the particles either carried a huge charge, or were a thousand times smaller than a hydrogen ion. They were too small to have their mass or charge calculated directly, but he attempted to deduce this from how much the particles were bent by electrical currents, of varying strengths. He decided to try to work out the nature of the particles.

#JJ THOMSON CATHODE RAY EXPERIMENT SUMMARY SERIES#

Many great scientific discoveries involve performing a series of interconnected experiments, gradually accumulating data and proving a hypothesis. The third experiment was a brilliant piece of scientific deduction and shows how a series of experiments can gradually uncover truths. This result was a major discovery in itself, but Thomson resolved to understand more about the nature of these particles. Halfway down the tube were two electric plates, producing a positive anode and a negative cathode, which he hoped would deflect the rays.Īs he expected, the rays were deflected by the electric charge, proving beyond doubt that the rays were made up of charged particles carrying a negative charge. To prove this hypothesis, he attempted to deflect them with an electric field.Įarlier experiments had failed to back this up, but Thomson thought that the vacuum in the tube was not good enough, and found ways to improve greatly the quality.įor this, he constructed a slightly different cathode ray tube, with a fluorescent coating at one end and a near perfect vacuum. Like all great scientists, he did not stop there, and developed the second stage of the experiment, to prove that the rays carried a negative charge. This proved that the negative charge and the ray were inseparable and intertwined. He found that by applying a magnetic field across the tube, there was no activity recorded by the electrometers and so the charge had been bent away by the magnet.

This cylinder had two slits in it, leading to electrometers, which could measure small electric charges. His first experiment was to build a cathode ray tube with a metal cylinder on the end. Thomson had an inkling that the ‘rays’ emitted from the electron gun were inseparable from the latent charge, and decided to try and prove this by using a magnetic field. Thomson constructed some elegant experiments to find a definitive and comprehensive answer about the nature of cathode rays. They debated whether the rays were waves or particles, as they seemed to exhibit some of the properties of both. Physicists knew that the ray carried a negative charge but were not sure whether the charge could be separated from the ray. However, other researchers, notably Crookes, argued that the focused nature of the beam meant that they had to be particles. With more experimentation, researchers found that the ‘cathode rays’ emitted from the cathode could not move around solid objects and so traveled in straight lines, a property of waves. William Crookes discovered that a tube coated in a fluorescing material at the positive end, would produce a focused ‘dot’ when rays from the electron gun hit it. Later and improved cathode ray experiments found that certain types of glass produced a fluorescent glow at the positive end of the tube.

This cathode ray also became known as an ‘electron gun’. Physicists in the 19th century found out that if they constructed a glass tube with wires inserted in both ends, and pumped out as much of the air as they could, an electric charge passed across the tube from the wires would create a fluorescent glow.

Look at any glowing neon sign or any ‘old-fashioned’ television set, and you are looking at the modern descendants of the cathode ray tube. Even without consciously realizing it, most of us are already aware of what a cathode ray tube is.

Jj thomson cathode ray experiment summary