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1026902-Nota-Padat-Fizik-F5-Electronic

1026902-Nota-Padat-Fizik-F5-Electronic - 9.1 CATHODE RAY...

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9.1 CATHODE RAY OSCILLOSCOPE What is thermionic emission? Thermionic emission is the process of emission of electrons from a heated metal’s surface. How does thermionic emission occur? Metal consists of a large number of electrons which are free to move. At room temperature, the electrons are free to move but remain inside the metal. The electrons cannot escape at the surface because they are held back by the attractive forces of the atomic nucleus. If the metal is heated at a high temperature, some of the free electrons may gain sufficient energy to escape from the metal. What is cathode rays? Thermionic emissions can be used to produce a continuous flow of electrons in a cathode ray tube. When the cathode is connected to the anode by an extra high tension (EHT) voltage supply, a narrow beam of fast electrons will move to the anode. The beam of electrons moving from the cathode to the anode is called cathode rays . Describe the properties of cathode rays Cathode rays can be used in picture tube of a television, a cathode ray oscilloscope and the visual display on a radar screen. The properties of cathode rays can be summarized: 1. Negatively charged particles called electrons. 2. Travel in straight lines and cast sharp shadows. 3. Travel at very high speed and have kinetic energy. 97
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