# [Amps] Capacitance Amount Formula

on4kj on4kj at skynet.be
Mon Feb 10 21:53:11 EST 2003

```I agree Eric,.

I retained from my professional live, ( 69 yy now )
Mathematicians say 7 x 7 = 49 no discussion possible....
Biologist say 7 x 7 = between  48,99 and 49,01
While commercial people say today 7 x 7 = anything below 40, tomorrow it can
be anything over 60.
Just take care who handles the numbers.
My rule of thumb.

73 Jos on4kj

----- Original Message -----
From: <MorgusMagnificen at aol.com>
To: <davek at medphys.ucl.ac.uk>
Cc: <amps at contesting.com>
Sent: Monday, February 10, 2003 4:05 PM
Subject: Re: [Amps] Capacitance Amount Formula

> 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
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>

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