+1
Actually, the answer to everything is 42.
Of the Original Series... the subsequent series played kind of loose with science (worse than the original, I should say).Stone:
Take some university physics courses and you will find that what you say here isn't actually true.
Or for that matter, watch a few Star Trek episodes.
SPL can be measured at any distance. It's usually one metre and one watt to work out speaker efficiency.
Steve.
He didn't really give a detailed answer... This was his reply....
There is always a physical limitation to a light source, which itself has an associated radius. So in practice this mathematical situation never arises. But theoretically, yes.
"Stone wrote:
So, on the photo forum, this question arose....
This is confusing me
according to the inverse square lawB=I/d^2,theIllumination from a light sourcequadruples every time the distance from subject to light source is cut in half.Inconsequence doesn't that mean that the light source approaches infinite intensitywhen the distance to the light source approaches '0'?Hoew can this be?is there a flaw in the inverse square lawor is it limited to certain conditions?:confused: "
My dad is a real honest to god physicist... I'll ask him tomorrow...
He didn't really give a detailed answer... This was his reply....
There is always a physical limitation to a light source, which itself has an associated radius. So in practice this mathematical situation never arises. But theoretically, yes.
"Stone wrote:
So, on the photo forum, this question arose....
This is confusing me
according to the inverse square lawB=I/d^2,theIllumination from a light sourcequadruples every time the distance from subject to light source is cut in half.Inconsequence doesn't that mean that the light source approaches infinite intensitywhen the distance to the light source approaches '0'?Hoew can this be?is there a flaw in the inverse square lawor is it limited to certain conditions?:confused: "
Infinitely bright point light sources are rarely encountered in practical photography. Therefore, theoretical formulas beloved by some physicists have little places in a photo forum. Our light sources are modified by reflectors and lenses, and the environment also influences the amount of light on a subject. Get practical: get a light meter.
It's limited by the real world application of the math.
In Physics, theories and laws seem to be based off of perfect conditions. There is no true point light source possible-- as it would occupy no space. As mentioned before, other effects start happening with different light sources as you get really close. There is no problem with the law, but perfect conditions for it are never attained in real life.
Well, because light sources aren't infinitely "Intense".
It might be easier to understand by starting at the light source, which has a given intensity which is the high limit (not infinity), and then doing the math as you move away from the source.
Good point. Another way of stating this idea is that at zero distance, the light intensity would not be infinite, but at MAXIMUM, and depend on the FINITE intensity of the light source.
As the distance approaches zero, the intensity asymptotically approaches infinity. You can never reach zero distance.
He didn't really give a detailed answer... This was his reply....
There is always a physical limitation to a light source, which itself has an associated radius. So in practice this mathematical situation never arises. But theoretically, yes.
"Stone wrote:
So, on the photo forum, this question arose....
This is confusing me
according to the inverse square lawB=I/d^2,theIllumination from a light sourcequadruples every time the distance from subject to light source is cut in half.Inconsequence doesn't that mean that the light source approaches infinite intensitywhen the distance to the light source approaches '0'?Hoew can this be?is there a flaw in the inverse square lawor is it limited to certain conditions?:confused: "
But still this contradicts the idea of a limited intensity.
Disclaimer: I'm trained as a mathematician, not a physicist; though if I'd had an undergrad minor it would have been physics.
-NT
"That's one of the problems in physics, the electron is supposedly a point particle, and the charge self repulsion energy is greater than the mass of the particle itself, whenever you deal with point entities and forces or fields you can get infinities which make no physical sense, in other words physical solutions always have a radius".
He additionally said...
"The 1 / R^2 rule does not apply when one goes down to single photon interactions."
Was his second response ...
Referring back to the OP - it is a good question , relevant for macro flash.
I think the Gauss Law still applies, but you have to consider the source with real dimensions.
This can be done by the integral calculus -conceptually, by applying Gauss law to many small illuminated points.
I hope my scribble is legible. It is for a 2 dimensional "flash tube" - approximately OK for a thin rectangular flash
and could be expanded to a 3D flash reflector.
But still this contradicts the idea of a limited intensity. The problem seems to be in the definition of intensity.
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