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Re: Battery connection



.... also it is customary to draw the cells with the lines horizontal.
Horowitz and Hill and Costco have finally driven the nails in the coffin of
the original definition of battery. H&W use cell and battery nearly
interchangeably, and Costco clearly labels their cells, battery.

I will not use the word for a collection of objects for a single one.

B.W. like L. Kow. must not be young, as they, and I, persist in correct usage.

Panzers,

bc




brian whatcott wrote:

At 08:42 8/3/01 -0700, Julie wrote:

Dear all,
Encountered this problem which i am not very sure. Please enlighten.
If two batteries are connected in parallel (1.5V and 3.0 V), and the =
connection is such that the same terminals are
(a) at the same side
I
--------I I -------
I 3.0 V

I
--------I I ---------
I 1.5V


(b) opposite side,=20
I
--------I I -------
I 3.0 V

I
--------I I ---------
I 1.5V

the former circuit would have an effective voltage of 1.5 V, but the =
latter? Why?
Thanks.
Julie

Sometimes, the internal resistance of cells and batteries of cells
is unimportant: this time though, it matters.

We suppose that the internal resistance R is proportional to its
terminal voltage - for no very fundamental reason, save that the battery
of two cells may be using the same type cell as the single cell.

In case (a) we work the current first:
I = e/r = (3-1.5)/(R+2R) = 1.5/3R

Now we are in a position to estimate the external voltage:
for the single cell (it is the same as the double cells)
e = 1.5 + 1.5R /3R = 2 volts.
You can see the combined terminal voltage would vary with the internal
resistance ratios.

I believe you are now in a position to work out the larger current
flowing though the two cells in case (b) and then derive its terminal
volts for the same assumptions.

Useless factoid of the day: one convention for cell graphics is to show the
positive electrode at the LONGER bar of the two. Thought you'd want to
know....

brian whatcott <inet@intellisys.net> Altus OK
Eureka!