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CHAPTER 19 THERMIONIC EMISSION ------------------------------------------------- Top of Form 1. | consume of a nothingness diode|  | Thermionic Emission: * The release of electrons from the muster of a metal, when it is heated to a high temperature, is called thermionic emission. The electrons, so emitted, be known as thermions. * The minimum vigor required to change state an electron from the metal surface is called the work flow of that metal. For example, caesium has the lowest work function at W0 = 1.75 eV, tungsten has a work function of 4.55 eV. | | 2.| Diode: Construction and Working|  | | The dickens electrodes: 1. Cathode: Cathode is a metal piston chamber coated with oxides of BaO or SrO, which pester the filum in the indirectly heated lawsuit of rectifying tubes. In the directly heated type of diodes, filament itself serves as a cathode. The cathode emits electrons when heated. 2. Anode (or exfoliation): It is a cyli nder enclosing the cathode. It collects electrons. | | 3.| Diode Characteristics|  | The circuit plot | | Circuit used for studying the characteristic curves of a vacuum diode| i. Keeping filament reliable If constant, change in home office current (Ip), is observed when habitation voltage (Vp) is steadily increased. (Plate characteristics) ii.

dance shade (i) is repeated for different constant values of If. i.e.If1, If2, If3 etc. The graphs representing these observations ar shown below. These curves are known as static characteristics of diodes. | Study of Characteristics (Conclusions) A fixed number of electrons are emitted per second by the cathode , when a constant current If is passed throu! gh the filament. For a small plate voltage, * Only a few electrons reach the plate; Ip is small. * The remaining electrons gather between the cathode and the plate and form a cloud known as space charge. Space arouse In a vacuum diode, the heated cathode emits electrons. These electrons are attracted by...If you emergency to frustrate a full essay, order it on our website: OrderEssay.net

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