Light

Newton's Experiment: He showed that the colors formed by sunlight going through a prism are NOT due to differences in absorption of the light by the prism (as was thought at that time). He argued that white light is composed of the union of all the colors of the spectrum.


Properties of light.
Light has wave and particle behavior.
Wavelength of light: the length of a single light wave (distance from crest to crest).
Frequency of light: number of waves per second (or other time measurement for that matter). It is usually measured in Hertz=1/sec .

So we have:

c = ln

where l = wavelength, n = frequency, and c = speed of light.

Recall Einstein's formula:

This implies that the higher the frequency and hence the lower the wavelength then the more the energy. Various important parts of the spectrum include (from lowest to highest energy):


Photoelectric effect: explained by Einstein, referenced for his Nobel prize. Photons of sufficient energy (given by the E=hn formula) can knock out electron from certain (photosensitive) materials and produce a current.
So no current will be produced by light of frequency less than the critical E=hn associated with the energy E needed to knock out a single electron. Light of a frequency which exceeds this critical frequency will caused electrons to be emitted; the number of electron emitted depends on the intensity of the light.


LASER: Light Amplification by Stimulated Emission of Radiation. Electrons in a laser producing tube are "pumped" and elevated to higher energy orbitals. Photons at frequencies specific to the material trigger the emission of photons by electrons in these higher energy orbitals. Furthermore, the emitted photons are in phase with the triggering photons.


Greenhouse effect: sunlight passes through a "greenhouse material" such as regular greenhouse glass. The material is opaque to infrared (heat) radiation, so that the heating caused by the sunlight is trapped inside the greenhouse. (Example: greenhouse, car windows.)

Greenhouse gasses that are in the atmosphere: carbon dioxide, water, methane.


Ozone: The gas formed of three bounded oxygen atoms. In the upper atmosphere sufficiently energetic solar photon break apart oxygen molecules; then ozone it is formed by oxygen molecules combining with the free oxygen atoms. It is also naturally formed by lightning.
Ozone blocks ultraviolet radiation.
Cloroflorocarbons: industrial chemicals that catalyze the breakdown of ozone in the upper atmosphere.
Ozone hole: A region in the upper atmosphere over the Antarctic continent that is unusually depleted of atmospheric ozone.


Photosynthesis: the process by which green plants convert carbon dioxide plus water plus sunlight energy into glucose. The process is catalyzed by chlorophyll (the green stuff in plant leaves) and gives off oxygen.
Respiration: the process by which living organisms oxidize glucose (and related starches) to produce energy.
ATP (adenosine triphosphate): the organic molecule that organisms use for their energy requirements. It breaks down into ADP (adenosine diphosphate) + energy + a phosphate group.


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