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The Electron

The Electron. 27-1. Cathode Rays. 1870’s Sir William Crookes. Cathode Ray Tube. Vocabulary e – charge v – velocity B – magnetic field r – radius of curvature F mag = evB F = ma = mv 2 /r evB = mv 2 /r e/m = v/Br. Electron Deflection.

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The Electron

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  1. The Electron 27-1

  2. Cathode Rays 1870’s Sir William Crookes

  3. Cathode Ray Tube

  4. Vocabulary • e – charge • v – velocity • B – magnetic field • r – radius of curvature • Fmag = evB • F = ma = mv2/r • evB = mv2/r • e/m = v/Br Electron Deflection

  5. An electric field can be applied so that the resultant force is equal and opposite to the magnetic force • Fel = eE • Fmag = evB • Fmag = Fel\eE = evB • v = E/B • Combined with e/m = v/Br • e/m = E/B2r • The electrical and magnetic fields and radius can all be measured Electron Deflection

  6. e/m had been found • Could not be separated • e/m = 1.76 x 1011 C/kg Electron Deflection

  7. Millikin’s Oil Drop

  8. Fg = mdrg (down) • Fe = qE (up) • Fg= Fe\ mdrg = qE • q = mdrg/E • q was found to always be an integer multiple of e • e = 1.6 x 10-19 C • The modern value of e is 1.602 x 10-19 C Millikin’s Oil Drop

  9. Hot, Dense objects emit radiation whose wavelength is inversely proportional to their temperature • This is called blackbody radiation • Wien’s Law • λpT = 2.90 x 10-3 mK • At 300K, we are not aware of the radiation • At 1000K things glow a dull red • At 2000K things begin to appear “white hot” • The 6000K peak is the upper end of the visible spectrum Blackbody Radiation

  10. Blackbody Radiation

  11. Vibrational Energy of molecules is a multiple of a minimum energy • It is quantized • E = hf • h = 6.626 x 10-34 Js • E = nhf , n = 1,2,3… • h is now known as Planck’s Constant • hc = 1240 eVnm Planck’s Quantum Hypothesis

  12. 1858 – 1947 • Nobel Prize in Physics 1918 • Max Planck Medal 1929 • Shared with Einstein • Worked with Bohr, Heisenberg and Pauli – Copenhagen Interpretation • Thought wave mechanics would render quantum theory useless • Quantum theory stands today Max Planck

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