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As the first half wavelength of the approaching wavefront reaches the atom PowerPoint Presentation
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As the first half wavelength of the approaching wavefront reaches the atom

As the first half wavelength of the approaching wavefront reaches the atom

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As the first half wavelength of the approaching wavefront reaches the atom

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  1. As the first half wavelength of the approaching wavefront reaches the atom shown, the E-field E c B 1) pushes the electron cloud up, the nucleus down. 2) pushes the electron cloud left, the nucleus right. 3) pushes the electron cloud right, the nucleus left. 4) pushes the electron cloud down, the nucleus up.

  2. As the electrons move down under the influence of the E-field, the oncoming B-field in the same half wavelength pushes those electrons E 1) toward the right of the screen. 2) toward the left of the screen. 3) up. 4) down. 5) forward, in the direction of c. 6) backward, into the screen. c B

  3. As the protons move up under the influence of the E-field, the oncoming B-field in the same half wavelength pushes those protons E 1) toward the right of the screen. 2) toward the left of the screen. 3) up. 4) down. 5) forward, in the direction of c. 6) backward, into the screen. c B

  4. Recall 1 2 1 2 1 2 1 2 Energy stored in the electric field within a capacitor: CV2 withC = oA/d and V=Ed so PEEfield = (oA/d)(Ed)2 = o(Ad)E2 1 2 1 2 uE= oE2 Similarly Energy stored in the magnetic field of a solenoid: LI2 whereL = NBA/Iand B=moI(N/) 1 2 so PEBfield = (NBA/I)I2 = NBA(B/moN)2 1 2mo PEBfield = (A)B2 uB= B2 We say the “energy density” within the magnetic field is 1 2mo

  5. A A cDt During a time Dt, an electromagnetic wave will deliver energy to/through any surface A it illuminates: AcDt(uB+ uB )

  6. Energy transport (intensity) of EM waves The rate at which electromagnetic energy is being transferred by an EM wave through a certain area is: Units: W / m2 Remember! E and B fields fluctuate with time!

  7. Compared to wave 1, the power transported by wave 2 is about 1) half 2) the same 3) double 4) quadruple

  8. You should recall that the time average of E(t) is zero. 1 4 1 2 1 2 1 2 Eo2sin 2 Eo Eosin Eo 2 Eosin What is the average E2(t)? • 0 • Eo • Eo • 4) Eo • ( Eo)2 • Eo2

  9. 0 0 0 0 < Emax2 / oc < Emax2 / oc < Emax < Emax Emax2 / oc Emax2 / oc Emax Emax Average Intensity and RMS values Energy delivered E field Because intensity is constantly changing, we work with the average intensity Average over one full wavelength. Since E varies sinusoidally, (E2)avg = (1/2)(Emax2).

  10. Atomic Spectra But spectrum of a heated rarefied gas shows lines: Emission spectrum And when white light shines through a rarefied gas, dark lines appear in the continuous spectrum: Absorption spectrum Blackbody spectrum is continuous: Explaining these phenomena requires and understanding of the atom

  11. Energy Levels for Hydrogen

  12. 1 2 Some answers to previous slides: 1) pushes the electron cloud up, the nucleus down 5) forward, in the direction of c. 5) forward, in the direction of c. 4) quadruple 6)Eo2