[Amps] Capacitance Amount Formula

[MorgusMagnificen at aol.com]

Yes, I do think you are wrong. The concept of 'exact' is context sensitive, 
but not altogether meaningless. This is an issue which causes scientists to 
have a great problem communicating with the scientifically illiterate world.

For practical purposes, I would call an exact analysis/calculation  one whose 
errors can be specified. "Exact" means that the results which we state are 
less than the precribed error. If you insist that the error go right down to 
zero, then there is nothing in the world that can be specified that precisely 
(this is the uncertainty principle in action). Does that mean that we totally 
abandon the concept of exact? Let me give some familiar examples.

Suppose I go into a high-precision laboratory and measure the voltage across 
the terminals of a standard cell and report it as 1.376899 volts +/-.000001 
volt (this is doable.) Are you rejecting this as non-exact because I cannot 
get closer than 1uVolt?

The degree of error is the whole gist of exactness, and in practice, we refer 
to measurments, calculations, etc. as 'exact' if their error is very low. How 
low? That requires judgement and adherence to convention.

In the case which I stated (a power supply calculation) I was making a fairly 
specific statement which would be understood by most experienced design 
engineers. Namely, before the computer became a desktop tool for every single 
person on the planet, many conceptually simple problems were never solved 
exactly. The most important category of same is problems involving non-linear 
elements, which are not well described by standard physical laws and 
formulas. Pre-computer power supply design was based upon picewise-linear 
approximations to linear circuits, which means that even if the mathematics 
were done exactly, the results would still be approximate. But with a 
computer, you can easily solve the necessary circuit equations to any degree 
of precision, limited only by how many significant figures of precision you 
seek. In practice, we don't need 10 or 100 sig. figures to feel that the 
result is exact.

So in that respect, when I tell you that I have done an exact solution, what 
I am really saying (this is understood to those who do this kind of 
calculation) is I will calculate the results for you to any specified degree 
of precision. You CANNOT make that statement based on an old-style 
(non-numeric) calculation which invokes approximations in the basic circuit 
equations themselves (e.g. piecewise-linear models). That is the difference.

Eric vonValtier K8LV