Lect14 - Lecture 14, p 1 A vast time bubble has been...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Lecture 14, p 1 A vast time bubble has been projected into the future to the precise moment of the end of the universe. This is, of course, impossible.--D. Adams, T h e H i t c h h i k e r s G u i d e t o t h e G a l a x y There is light at the end of the tunnel.-- proverb The light at the end of the tunnel is just the light of an oncoming train.--R. Lowell Lecture 14, p 2 Lecture 14: Barrier Penetration and Tunneling x 0 L U x U(x) E U(x) x A B C B A nucleus Lecture 14, p 3 Act 0 The midterm exam was: a. Just right b. Too easy c. Too hard d. Too long e. Too long and too hard Lecture 14, p 4 The Most Difficult Midterm Question arm 1 laser 8 mW = 700 nm or 500 nm detector arm 2 1 2 3 4 Mirror position Detected Power (mW) a. b. c. Interference (of single photons and lots of photons) requires two (or more) indistinguishable processes. Lecture 14, p 5 Today Tunneling of quantum particles Scanning Tunneling Microscope (STM) Nuclear Decay Solar Fusion The Ammonia Maser The rest of the course: Next week : 3 dimensions - orbital and spin angular momentum H atom, exclusion principle, periodic table Last week : Molecules and solids. Metals, insulators, semiconductors, superconductors, lasers, . . Good web site for animations http://www.falstad.com/qm1d/ Lecture 14, p 6 Due to barrier penetration, the electron density of a metal actually extends outside the surface of the metal! E F Occupied levels Work function V o Assume that the work function (i.e., the energy difference between the most energetic conduction electrons and the potential barrier at the surface) of a certain metal is = 5 eV . Estimate the distance x outside the surface of the metal at which the electron probability density drops to 1/1000 of that just inside the metal. x = 0 x Leaky Particles: Revisited Lecture 14, p 7 Due to barrier penetration, the electron density of a metal actually extends outside the surface of the metal! E F Occupied levels Work function V o Assume that the work function (i.e., the energy difference between the most energetic conduction electrons and the potential barrier at the surface) of a certain metal is = 5 eV . Estimate the distance x outside the surface of the metal at which the electron probability density drops to 1/1000 of that just inside the metal. 2 2 2 ( ) 1 1000 (0) Kx x e - = x = 0 x 1 1 ln 0.3 2 1000 x nm K = - Leaky Particles: Revisited ( 29-1 2 2 2 2 2 5 2 2 11.5 nm 1.505 eV nm e e m m eV K V E h =- = = = Lecture 14, p 8 Tunneling: Key Points In quantum mechanics a particle can penetrate into a barrier where it would be classically forbidden....
View Full Document

Page1 / 28

Lect14 - Lecture 14, p 1 A vast time bubble has been...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online