When discussing the dispersion in gases, we model the gas molecule as a damped harmonic oscillator, and obtain the induced dipole moment by an incident EM wave. Since we know that an oscillating dipole will radiate, the gas molecule will scatter the incident wave by such re-radiation. (a) Find the general expression for the scattering cross section of the gas molecule.

(b) When considering the sunlight scattered by molecules in the atmosphere (known as the Rayleight scattering), we know that the sunlight frequency (optical range) is much smaller than the resonance frequency which is typically in the ultraviolet range, and we can further ignore the damping. Derive the approximation of the scattering cross section (textbook Eq. 10.41). The strong frequency dependence explains why the sky looks blue. Next let’s analyze the polarization of the scattered light. Consider the incident light traveling in the z direction.

(c) First, assume that the incident light is linearly polarized along the x axis. What is the polarization direction of the light scattered into the z direction and the y direction, respectively?

(d) Next, consider unpolarized incident light, i. e., its E^-> field direction remains in the x-y plane, but the exact orientation fluctuates randomly and uniformly along all directions in the x-y plane. Argue that the scattered light along the z-direction is also unpolarized, but the scattered light along the x and y directions is fully polarized. The scattered light along other directions is partially polarized.

This effect helps photographers to obtain a stronger contrast of the blue sky. Since the blue light scattered by the atmosphere is typically partially polarized while the scattered light by clouds is unpolarized (because such scattered light experiences multiple reflections and scatterings by the dense clouds thus loses its polarization), photographers use a polarizer to block the polarized blue light thus reduce the brightness of the blue (so the sky looks more blueish) which increases the contrast of the picture. Such effect is strongest when the camera is pointed at 90 degrees from the sunlight.

car stops. he keeps going = he has inertia

relativism, roughly put, is the view that truth and falsity, right and wrong, standards of reasoning, and procedures of justification are products of differing conventions and frameworks of assessment and that their authority is confined to the context giving rise to them. more precisely, “relativism” covers views which maintain that—at a high level of abstraction—at least some class of things have the properties they have (e.g., beautiful, morally good, epistemically justified) not simpliciter, but only relative to a given framework of assessment (e.g., local cultural norms, individual standards), and correspondingly, that the truth of claims attributing these properties holds only once the relevant framework of assessment is specified or supplied. relativists characteristically insist, furthermore, that if something is only relatively so, then there can be no framework-independent vantage point from which the matter of whether the thing in question is so can be established.

relativism has been, in its various guises, both one of the most popular and most reviled philosophical doctrines of our time. defenders see it as a harbinger of tolerance and the only ethical and epistemic stance worthy of the open-minded and tolerant. detractors dismiss it for its alleged incoherence and uncritical intellectual permissiveness. debates about relativism permeate the whole spectrum of philosophical sub-disciplines. from ethics to epistemology, science to religion, political theory to ontology, theories of meaning and even logic, philosophy has felt the need to respond to this heady and seemingly subversive idea. discussions of relativism often also invoke considerations relevant to the very nature and methodology of philosophy and to the division between the so-called “analytic and continental” camps in philosophy. and yet, despite a long history of debate going back to plato and an increasingly large body of writing, it is still difficult to come to an agreed definition of what, at its core, relativism is, and what philosophical import it has. this entry attempts to provide a broad account of the many ways in which “relativism” has been defined, explained, defended and criticized.

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