Thomson verified that cath had both magnetic and electric fields, collected the rays in a metal cup, and discovered an overabundance of negative charge. Thomson built on William Crookes's experiments with gas discharge tubes, and through his experiments, he made several significant discoveries. How were cathode rays used in the discovery of the electron? William Crookes, after whom the tube was initially named, observed that these particles carry momentum, which can be altered by a magnetic field, as shown in the image below.Ĭheck out our explanation on Momentum. The name cathode ray tube comes from the fact that the electrons are emitted from the cathode. These electrons excite the gas atoms, causing the emission of electromagnetic radiation, which makes the path of the electrons visible. When a voltage is applied across the electrodes, electrons are emitted from the cathode and accelerate towards the anode. The cathode ray tubeĬathode ray tubes, previously known as gas discharge tubes or Crookes tubes, are vacuum glass tubes with two metal electrodes and rarefied gas inside. Thomson in 1897 when he concluded that cathode rays were made up of a previously unidentified negatively charged particle, the electron. The most important use of cathode rays was discovered by J.J. Julius Plücker and Johann Wilhelm Hittorf first observed cathode rays in 1869, and Eugen Goldstein named them in 1876. The properties of cathode rays do not change regardless of the gas used in the tube. Properties of cathode raysĬathode rays are negatively charged particles that travel in a straight route and ionise the gas inside the vacuum tube. The electrode connected to the negative pole of the voltage source is the cathode, and the electrode connected to the positive pole of the voltage source is the anode. To find which electrode is the cathode and the anode, we need to look at the connections between the electrodes and the voltage supply. The electrons emitting from the cathode is what causes this glow. A glow behind the positive electrode (cathode) can be observed when a potential difference (voltage) is applied to the electrodes. These discharge tubes are devices that control the electric current between a potential difference applied to the electrodes in a high vacuum. If you want to know more about this discovery, then keep reading! What is a cathode ray?Ĭathode rays, also known as electron beams, are streams of electrons detected in discharge tubes (vacuum tubes). These rays played a significant role in discovering the electron. They are also known as e-beam or electron beams. Thomson was able to apply electric and magnetic fields to manipulate the rays, which eventually convinced the physics world that they were composed of tiny particles, electrons, opposed to waves in the now-rejected ether.įind out more about Thomson and the story of the first subatomic particle here, or visit the Museum to see Thomson’s cathode-ray tube in the Collider exhibition. If you’re interested in the details of how Thomson and Everett conducted their experiments visit the Cavendish Lab’s outreach page here.Cathode rays are basically electron streams found in vacuum tubes. Only when almost all the air has been removed to create a high vacuum – a state that would shatter ordinary glass vessels – can the rays travel the full length of the tube without bumping into air molecules. The quality of Everett’s glassblowing was absolutely crucial for the experiments to work.Ĭathode-rays are produced when an electric current is passed through a vacuum tube. Everett made all of Thomson’s apparatus, and was responsible for operating it – in fact, he generally forbade Thomson from touching anything delicate on the grounds that he was “exceptionally helpless with his hands”. Cambridge’s Cavendish Laboratory, where Thomson spent his scientific career, also has an original tube in its collection.Įach tube was custom-made by Thomson’s talented assistant, Ebenezer Everett, a self-taught glassblower. Using more than one cathode-ray tube in 1897 for his experiments, Thomson managed to identify a particle 1,000 times smaller than the then known smallest piece of matter: a hydrogen atom. I had read lots about Thomson’s famous experiments on the electron – the first subatomic particle to be discovered – but to actually see and touch his apparatus myself, to notice the blackened glass and the tube’s minute features that are omitted in books, brought the object to life. Holding the delicate glass cathode-ray tube in my hands, once used by the great physicist JJ Thomson, was an incredible treat, and an experience I will never forget. Rupert Cole celebrates JJ Thomson’s birthday with a look at one of the star objects in our Collider exhibition. Rupert Cole celebrates JJ Thomson's birthday with a look at one of the star objects in our Collider exhibition.
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