Phy107Lect24

Phy107Lect24 - Wed. Nov 3 Phy107 Lecture 24 From Last...

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: Wed. Nov 3 Phy107 Lecture 24 From Last Time… • All objects show both wave-like properties and particle-like properties. • Electromagnetic radiation (e.g. light) shows interference effects (wave-like properties), but also comes in discrete photons of energy hf (particle-like properties) • Matter clearly shows particle-like properties, but also shows interference and diffraction effects (wave-like properties). Wed. Nov 3 Phy107 Lecture 24 Electron diffraction • Wavelength determined by electron momentum • Momentum determined by electron energy • Energy determined by accelerating voltage (energy in electron-volts ( eV ) = voltage) Wavelength = Planck's constant momentum 1.23 eV 1/2 − nm E kinetic Wavelength in nm = Energy in eV Wed. Nov 3 Phy107 Lecture 24 • Increasing the energy decreases the wavelength. • When electron wavelength comparable to differences in path length, destructive interference can occur. • Appears as spatial directions in which reflected electrons are never seen. 1.23 eV 1/2 − nm E kinetic Wavelength in nm = Wed. Nov 3 Phy107 Lecture 24 Making a particle out of waves 440 Hz + 439 Hz 440 Hz + 439 Hz + 438 Hz 440 Hz + 439 Hz + 438 Hz + 437 Hz + 436 Hz Wed. Nov 3 Phy107 Lecture 24 Using quantum mechanics • Quantum mechanics makes astonishingly accurate predictions of the physical world • Can apply to atoms, molecules, solids. • An early success was in understanding – Structure of atoms – Interaction of electromagnetic radiation with atoms Wed. Nov 3 Phy107 Lecture 24 Planetary model of atom • Positive charge is concentrated in the center of the atom ( nucleus ) • Atom has zero net charge: – Positive charge in nucleus cancels negative electron charges. • Electrons orbit the nucleus like planets orbit the sun • (Attractive) Coulomb force plays role of gravity nucleus electrons Wed. Nov 3 Phy107 Lecture 24 Planetary model Coulomb force Orbital speed • Bohr also retained the particle picture. • Since electron is in a circular orbit, it’s velocity is continually changing direction (centripetal acceleration = v 2 / r ) • The source of this acceleration is the Coulomb force between the positive nucleus and the negative electron ke 2 /r 2 acceleration = v 2 r = Force mass = k e 2 mr 2 Wed. Nov 3 Phy107 Lecture 24 Difference between atoms • No net charge to atom – number of orbiting negative electrons same as number of positive protons in nucleus – Different elements have different number of orbiting electrons • Hydrogen: 1 electron • Helium: 2 electrons • Copper: 29 electrons • Uranium: 92 electrons!...
View Full Document

This note was uploaded on 01/05/2012 for the course PHYS 107 taught by Professor N/a during the Spring '08 term at Wisconsin.

Page1 / 35

Phy107Lect24 - Wed. Nov 3 Phy107 Lecture 24 From Last...

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