5: Thermionic Emission - Tools for Science

5: Thermionic EmissionPurposeWhile we think of quantum mechanics being best demonstratedin processes that showdiscontinuous change, historically quantum mechanics wasfirst revealed in systems wherea large number of particles washed out the jumps: blackbody radiation and thermionicemission. In this lab you will investigate these two phenomena in addition to classicalspace-charge limited electron Emission : Child s , as demonstrated by their ability to conduct an electric current, contain mobileelectrons. (Most electrons in metals, particularly the core electrons closest to the nucleus,aretightly bound to individual atoms; it is only the outermost valence electrons that aresomewhat free .) These free electrons are generally confined to the bulk of the metal. Asyou learned in E&M, an electron attempting to leave a conductor experiences a strong forceattracting it back towards the conductor due to an image charge:Fx= e24 0(2x)2( )wherexis the distance the electron is from the interface andeis the absolute value of thecharge on an electron.

104 Thermionic Emission or dV dx = v u u t 4J A ǫ 0 q 2e m V1 4 (5.14) This differential equation is separable: dV V1 4 = v u u t 4J A ǫ 0 q 2e m dx (5.15) V3 4 3 4 = v u u t 4J A ǫ 0 q 2e m x (5.16)

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  Emissions, Thermionic emission, Thermionic

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