Re: voltages etc.

[Joseph Bellina <jbellina@SAINTMARYS.EDU>]

Part one,
You can measure the potential difference across the terminals of the
battery in such a way that no current flows.  That says that the
potential difference exists whether or not current is flowing.  I could
make the argument on more theoretical grounds and no doubt others will,
but for your colleague, I suspect the measurement claim will be more
convincing.
Part two
If there is no conducting path between the negative terminal of the
battery and ground (a separate place, distinct from the battery
terminals) then there is no complete circuit and the positive terminal
and the bulb are at the same potential as the ground.  The negative
terminal is therefore some 6 volts or so negative with respect to
ground.

hope that helps.

joe

On Mon, 3 Mar 2003, Seth T Miller wrote:

> Hello all,
>
> I have a question, actually two, that I am discussing with another
> faculty member.
>
> Part One:
> Take a 6 volt dry cell battery.  My colleague opines that one cannot
> speak rightly of a voltage existing between the two sides of the battery
> until the terminals are connected, thus completing the circuit.  Her
> reasoning is that the chemical reaction is the source of the voltage and
> does not occur unless the terminals are connected in a circuit (except
> perhaps in very small amounts as batteries run down when left to stand).
>
> Is this a correct analysis or can we rightfully speak of a voltage
> difference between the two sides of a battery, and if so is it 6 volts
> in this case?
>
>
> Part Two:
> My colleague connected the positive side of a 6 volt dry cell battery to
> a 1.5 volt light bulb, then connected the other side of the light bulb
> to the ground.  The bulb does not light.  Is there a voltage difference
> between the positive side of the battery and the ground and if so is it
> 6 volts?  Why doesn't the bulb light?
>
> Her latest theory is that as soon as one touches the positive side of
> the battery, any excess charges are immediately drained off and that
> side of the battery becomes equalized with the ground.  The chemical
> reaction is not occurring, so there is no way for a voltage difference
> between the positive terminal and the ground to be maintained, thus the
> bulb does not light.
>
> Is this a correct analysis?  How could it be analyzed in more detail?
>
> Thank you-
> -Seth Miller

Joseph J. Bellina, Jr.               574-284-4662
Associate Professor of Physics
Saint Mary's College
Notre Dame, IN 46556