TimR wrote:
On Friday, May 22, 2015 at 1:37:48 PM UTC-4, dadiOH wrote:
TimR wrote:
On Friday, May 22, 2015 at 10:17:14 AM UTC-4, Scott Lurndal wrote:
Visible light decreases with the square
"inverse square law". Wonder why magnetism
would be different?


Because it doesn't.

Visible light does not decrease with the inverse square rule.

Visible light from a point source decreases with the inverse square
rule.

Visible light from a line source like a fluorescent tube decreases
with a simple inverse, no square involved, rule. Until you get far
enough away that a line source appears to be a point.

Visible light from a plane source doesn't decrease at all, until you
get far enough away that it appears to be a point.

I'm reasonably sure that those seeming contradictions are because a
given
point is receiving light from many areas of the large source. If one
were to
measure the light fall off of each of those areas, the inverse
square rule
would be true.

It's called math.

Weren't you required to derive the inverse square rule at some point?
It's a straightforward application of geometry.

I don't recall having to do so but I used it daily for more than 40 years.

But you always have to check your assumptions. Those assumptions
require a point source, or a reasonable approximation.

Indeed. Small enough so the light doesn't "wrap". Or distance...the sun is
a "point source". In practical terms, source size relative to subject size.