Re: electronic components

[John Mallinckrodt <ajmallinckro@CSUPomona.Edu>]

Ludwik,

When I fit exponential functions to either of your sets of current data
and integrate them, I get charges of just under 6 C--not different enough
from the nominal 5 C to concern me greatly.  In your message of 12/26 you
say that you get your value from a *linear* fit to the data.  If so, that
certainly would explain the problem! 

Beyond that I don't have the answers you seek, but I am not at all
surprised that capacitors have properties that don't match our textbook
ideals.  Some of these are likely the result of hysteresis resulting from
residual polarization in the dielectric.  In any event the behavior here
is close enough to that of a 1 F cap to satisfy requirements in most
circuits.

John

On Sun, 29 Dec 1996 kowalskil@alpha.montclair.edu wrote:

> On 12/26/96 I was trying to understand the discharge curve of a 1-farad 
> capacitor. Here I will comment on the charging data which are shown below
> (the abbreviated table). The data refer to the same NEC capacitor as before. 
>
>       t (s)   0   50  100  150  200  250   400   500  1000  2000
>       I(mA)  40   27   20   14   10  6.4   3.2   2.0   0.8   0.4
>
> Here again the I=f(t) curve is not exponential (not a straight line on the 
> semi-log paper for all values of I). And the area under the curve shows that 
> the charge received is larger than Q=C*V=1*5=5 coulombs. As a matter of fact, 
> the charge flowing IN during the first 500 seconds was 11.4 coulombs while 
> the charge flowing OUT, during the same period, was 10.5 coulombs.


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