Light
A beam of monochromatic light is described using waves made up of oscillating electric and magnetic fields.
It can also be described using packets of energy (photons).
The two descriptions are related by
E = hf
where E is the energy of the photon, f is the frequency of the oscillation, and h is Planck's constant.
The energy can also be expressed in terms of the wavelength l or wave number w, using
l = c/f = 1/w
where c is the velocity of light.
PC Fig. 6.1 contains terms used for various regions of the continuous spectrum.
In order of increasing energy, these energies correspond to the spacing of energy levels for the following features of molecules:
Higher energy radiation can produce structural changes in polymers. That topic is not covered here; for an introduction to the effects of electron beams and gamma rays, see Dawes, K.; Glover, L. C. Physical Properties of Polymers Handbook Mark, J. E., Ed., American Institute of Physics, 1996, p 557.
Light is monochromatic if all photons have the same energy. It is polychromatic otherwise.
The polarization of light is determined by the direction of oscillation of its electric field vector (which is in all cases perpendicular to the direction of propagation of the light beam).
- Circularly polarized. Electric field vector rotates, either clockwise or counterclockwise.
- Elliptically polarized. The electric field vectors describes an ellipse. This behavior results from the combination of two circularly polarized beams of the same frequency, but unequal intensity and opposite handedness.
- Plane polarized: Electric field vector oscillates in a plane. Its physical effects may be similar to those to two circularly polarized beams of the same intensity and frequency, but opposite handedness.
- Unpolarized: Electric field vectors point in all directions perpendicular to the plane of propagation. The physical effects may be similar to that of two plane polarized beams of the same intensity and frequency, but with their planes of polarization separated by 90 deg.
The interaction of light with matter depends on E and its polarization.
Examples discussed elsewhere:
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September 14, 2001
Wayne L. Mattice: wlm@polymer.uakron.edu