Senior Lecturer Education Education: PhD, Physics, Georgia Institute of Technology Research Research Interests: GR, QM, nano. Selected Publications Selected Publications: Publications (via Google Scholar) Research Gate POPULAR PHYSICS: OPTICS: Crescent Formation During Partial Solar Eclipse of 2024 Apr 08 3:04pm Athens GA OPTICS: On the origin of the index of refraction (a la Feynman). The figure below provides a physical explanation of the origin of the refractive index of a transparent material. When a plane EM wave encounters (at x = 0) a dielectric half-space, the net field inside, Einside (plotted in red), can be viewed as the superposition, Einside = Eincident + Erad , of the incident wave, Eincident = A cos(wt - kx) (black curve) , and the scattered field, Erad = (B x/lambda) cos(wt - kx - pi/2) (blue curve), which is due to harmonically driven radiating charges comprising the material. The amplitude of Erad increases linearly with x (as more and more layers of charges get involved) and is shifted in phase by a quarter-period relative to Eincident, in accordance with Feynman's formula given by Eq. (30.18) in vol. I of his Lectures on Physics. When the three fields are plotted together, one sees the effective shortening of the net wavelength relative to the original lambda, resulting in apparent phase velocity decrease ( vphase < c, normal refraction ), with no change in wave's frequency. In the case of abnormal refraction, Erad = (B x/lambda) cos(wt - kx + pi/2) , and we get an increase in phase velocity ( vphase > c ), as shown below:
