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Re: voltages etc.



Seth T Miller wrote:


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?


This is a neat question that students bring up all the time. The 6V is only
the potential difference between the ends of the battery - it does not refer
to an actual potential at either end. By attaching the positive terminal to
ground via the light bulb wires and filament, that terminal now has "ground"
potential (0 Volts reference) after a brief transient adjustment. The
negative terminal is now at -6V relative to ground. Current will not flow
through the bulb because the ground connection and the positive terminal of
the battery are at the same potential.

Bob at PC