Recent content by damosuz

  1. D

    Battery voltage increases when voltmeter connected

    When I connect a AA rechargeable battery directly to a voltmeter, voltage increases slowly, regardless of the way I connect it. I can't figure out why.
  2. D

    Mechanism for extinction by scattering?

    I think I found the answer. It seems like you cannot get destructive interference with a single molecule, but if you consider a large plane of such molecules oscillating in phase, then you can show that the E-field produced by the plane will be at 180° with the velocity of the electrons. If you...
  3. D

    Mechanism for extinction by scattering?

    You mean it follows the force in the sense that its position will be positive if force is positive, right? Which means acceleration will be 180° with the force...
  4. D

    Mechanism for extinction by scattering?

    Electron accelerates at 180° with the force, but force is 180° with incident E-field, so acceleration (and emitted E-field) is in phase with incident E-field.
  5. D

    Mechanism for extinction by scattering?

    If light frequency is way smaller than resonance frequency of electron in molecule, electron will oscillate in phase with the force, thus accelerate 180° with the force. The EM wave produced by the molecule will then be 180° with the force, thus in phase with the incident E-field. I agree that...
  6. D

    Mechanism for extinction by scattering?

    Let's say you have a monochromatic laser beam directed towards a light sensor. As you move the sensor away from the laser, the intensity read by the sensor will decrease because of scattering on air molecules (extinction). Since intensity is proportional to the square of the E-field amplitude of...
  7. D

    Light reflected 90° out of phase, not 180°

    Here: https://en.wikipedia.org/wiki/Refractive_index#Microscopic_explanation Feynman says same thing in his lectures.
  8. D

    Light reflected 90° out of phase, not 180°

    Classically, we explain why light appears to move slower in glass by saying that the electrons in glass emit a light wave which is 90° out of phase with the light wave shaking them. However, the electrons would have to emit this wave not only in the incident direction, but in the opposite...
  9. D

    Fresnel zone and reflection of light on surfaces

    Weisskopf talks about reflection on a transparent dielectric like glass.
  10. D

    Fresnel zone and reflection of light on surfaces

    Thank you for your answer. I think I found a way to make sense of the area of the zone where reflection occurs (if you compute the phase for every possible path from source to surface to observer and add them, only paths close to the center will contribute significantly to the sum and the area...
  11. D

    Fresnel zone and reflection of light on surfaces

    In a Scientific American article from 1968 in which he explains classically how light interacts with matter, Victor Weisskopf states that "the reflection of light on the surface of a solid or liquid involves only the oscillators (electrons) located in a small, pillbox-shaped volume at the...
  12. D

    Hoyle's calculation of 7.65 MeV level of carbon nucleus

    4,002602 u is helium-4 including mass of electrons, but at 100 MK, helium-4 must be completely ionized, so I guess you should take mass of alpha particle...
  13. D

    Hoyle's calculation of 7.65 MeV level of carbon nucleus

    Mass of helium-4 (4.0015 u) plus mass of beryllium-8 (8.0053 u) gives 12.0068 u, which is 6.35 MeV above fundamental level of carbon-12. For triple alpha process T= 100 MK, which corresponds to a kinetic energy of 2 x 3/2 kBT = 0.03 MeV for the particles. This amounts to 6.38 MeV, way below 7.65...
  14. D

    Why include a 1/2 factor in the drag equation?

    Why the 1/2 factor in the equation F_{R} = \frac{1}{2}\rho C_{d}A v^{2}? Why not just divide every C_{d} value found in tables by 2 and omit the 1/2 in the equation instead?
  15. D

    How Can I Build an AM Receiver with Limited Supplies?

    Even if the resistance of the 50 μH inductor is much lower than that of the 800 μH?
Back
Top