Re: Flash & RC circuits

[Richard Bowman <rbowman@BRIDGEWATER.EDU>]

Chuck Britton, in talking about a through-away camera, suggested we get
one at our local photo developer. Thanks for the suggestion. He then
wrote:

> Each unit uses a single AA cell to charge a hefty capacitor. The camera is
> easy to disassemble and the circuit is fairly straightforward. Just be
> careful NOT to get shocked by the high voltage capacitor. (~ 300 volts) We
> have evidence at our school that a direct shock is not fatal, but it does
> NOT feel good.

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.

Richard
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Dr. Richard L. Bowman
Chair, Dept. of Physics                  e-mail:  rbowman@bridgewater.edu
(and Dir. of Academic Computing)                     phone:  540-828-5441
Bridgewater College                                    FAX:  540-828-5479
Bridgewater, VA  22812               http://www.bridgewater.edu/~rbowman/
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