Re: Flash & RC circuits

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

Richard Bowman wrote:

> The voltage rating of the capacitor is not the critical factor. The
> voltage rating only tells us approximately at what voltage with the
> dielectric break down and begin to conduct. Connected to one 1.5 AA
> battery, the capacitor can only charge to 1.5 v. But the crucial fact is
> the amount of charge stored on the capacitor which can then be discharged
> rapidly by a human connecting across its ends. Thus a large current flow
> results. Remember that Q=CV. I have not looked at my disposable flash
> unit yet, but my guess is that the capacitance is in the millifarad range.
> Just
> a guess.

It seems to me that no matter how large C is the current
through a body will never be larger than from the electric
"battery" which charged it in the first place. I would not
worry about a danger at 1.5 V, even if C were very large.
But a power supply of 300 V, without a protection, can
be fatal. In this case the circuit resistance and the charge
Q becomes decisive factors.

Medical people, if my memory can be trusted, dose
capacitors in Joules of stored energy. So many Joules -->
small effect and so many --> big effect. Does somebody
know the actual values for typical medical (electric
shocks) effects?

Ludwik Kowalski


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