Transcription of 5: Thermionic Emission
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5: Thermionic Emission
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.
Thermionic Emission 103 where V(x) is the potential difference (“voltage”) at xand mis the mass of an electron. Because the accelerating electrons constitute a steady current (i.e., J
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