[Physltest] [Phys-L] Re: LED mini-flashlight price break

[John Denker <jsd@AV8N.COM>]

Daniel Price wrote:
> ... Demonstrating the photoelectric
> effect using a red tabletop laser vs. the violet LED against a sheet of
> phosphorescent material drew quite the gratifying reaction from a tough
> crowd.  ["So you think lasers are powerful, eh?  Let's compare..."]

I like it.  I wouldn't have thought of that.  The small size
of the LED flashlight really helps "sell" the contrast.

BTW I think it would be better to say "quantization of light
and of atomic energy levels" rather than saying "photoelectric
effect".  There's no photoelectric current produced anywhere
in the procedure as described.

Conceptually:
   photocurrent cutoff wavelength    -->-- quantization
   phosphorescence cutoff wavelength -->-- quantization
but that doesn't mean photocurrent is synonymous with
phosphorescence.  Here "-->--" means "demonstrates or
provides evidence for".

I hope this doesn't sound like a nit-pick;  I was having a
hard time understanding the demonstration until I surmised
that it didn't really involve the photoelectric effect.

=============================

On the broader topic of playing with colored lights, it's
great fun to shine three primary lights (red, green, blue)
on the same place at slightly different angles, and then
interpose shadow puppets.  You'll get at least three
different-colored shadows (cyan, magenta, yellow).

However be warned that a significant fraction of the
customers will not get it.  They will insist on calling
the cyan area "blue", not just when it is alone but even
when it is in side-by-side contrast with a blue area.
They are not color-blind, since they can see that the
two areas are distinct;  they are just vocabulary-impaired.

It's not just that they're untrained;  many of them
have been explicitly mis-trained.  There's about a 50/50
chance that when the kids were introduced to color theory,
they were told that the subtractive primaries were red,
yellow, and blue.  That is, magenta was mis-called red and
cyan was mis-called blue.  It makes my hair stand on end.
   http://www.google.com/search?q=paint+primary-color+yellow+k12
_______________________________________________
Phys-L mailing list
Phys-L@electron.physics.buffalo.edu
https://www.physics.buffalo.edu/mailman/listinfo/phys-l