Re: photoelectric effect

[brian whatcott <inet@INTELLISYS.NET>]

At 16:55 6/28/99 -0400, Sam Held wrote:

> I am quoting Tipler's latest book
> (ed. #4) - "The intensity of a light beam (energy per unit area per unit
> time) is the number of photons per unit area per unit of time times the
> energy of each photon."


I caught a newsgroup note mentioning this URL which sets out to harmonize
the use of terms like 'intensity'

 http://www.optics.arizona.edu/Palmer/rpfaq/rpfaq.htm

I'll quote a little of his content:
************************************************************************

 Radiant intensity is a SI derived unit and is measured in W/sr.
Intensity is power per unit solid angle. The symbol is I. Intensity is the
derivative of power with respect to solid angle, dF /dw. The integral of
radiant intensity over solid angle is power....
A great deal of confusion concerns the use and misuse of the term
intensity. Some folks use it for W/sr, some use it for W/m2 and others
use it for W/m2-sr. It is quite clearly defined in the SI
system, in the definition of the base unit of luminous intensity, the
candela. Some attempt to justify alternate uses by adding adjectives like
optical (used for W/m2) or specific (used for W/m2-sr), but this practice
only adds to the confusion.
... For an extended discussion, I wrote a paper entitled "Getting
Intense on Intensity" for Metrologia (official journal of the BIPM) and
 a letter to OSA's "Optics and Photonics News", with a modified version
available on the web.

Photon quantities are also common. They are related to the radiometric
quantities by the relationship Qp = hc/l where Qp is the energy of a
photon at wavelength l , h is Planck's constant and c is the velocity
of light. At a wavelength of 1 m m, there are approximately 5*10^18 photons
per second in a watt. Conversely, also at 1 m m, 1 photon has an energy
of 2*10^–19 joules (watt-sec).
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brian whatcott <inet@intellisys.net>
Altus OK