Researchers noticed that objects placed in the tube in front of the cathode could cast a shadow on the glowing wall, and realized that something must be traveling in straight lines from the cathode. Cathode rays are invisible, but their presence was first detected in these Crookes tubes when they struck the glass wall of the tube, exciting the atoms of the glass coating and causing them to emit light, a glow called fluorescence. The voltage applied between the electrodes accelerates these low mass particles to high velocities. They travel in parallel lines through the empty tube. Since the electrons have a negative charge, they are repelled by the negative cathode and attracted to the positive anode. The increased random heat motion of the filament knocks electrons out of the surface of the filament, into the evacuated space of the tube. Modern vacuum tubes use thermionic emission, in which the cathode is made of a thin wire filament which is heated by a separate electric current passing through it. The positive ions were accelerated by the electric field toward the cathode, and when they collided with it they knocked electrons out of its surface these were the cathode rays. In the early experimental cold cathode vacuum tubes in which cathode rays were discovered, called Crookes tubes, this was done by using a high electrical potential of thousands of volts between the anode and the cathode to ionize the residual gas atoms in the tube. To release electrons into the tube, they first must be detached from the atoms of the cathode. The Maltese cross has no external electrical connection.Ĭathode rays are so named because they are emitted by the negative electrode, or cathode, in a vacuum tube. Cathode-ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen.Ī diagram showing a Crookes tube connected to a high voltage supply. Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the electron. They were first observed in 1859 by German physicist Julius Plücker and Johann Wilhelm Hittorf, and were named in 1876 by Eugen Goldstein Kathodenstrahlen, or cathode rays.
If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to electrons emitted from the cathode (the electrode connected to the negative terminal of the voltage supply). Cathode rays are normally invisible in this Teltron tube demonstration, enough gas has been left in the tube for the gas atoms to luminesce when struck by the fast-moving electrons.Ĭathode rays or electron beam ( e-beam) are streams of electrons observed in discharge tubes. A beam of cathode rays in a vacuum tube bent into a circle by a magnetic field generated by a Helmholtz coil.
0 kommentar(er)
