At 11:49 +1100 12/11/97, Jerry McDonald wrote:
>I'm taking a class on electrical troubleshooting for work. The instructor
>asks which direction does electricity flow pos to neg or neg to pos? In my
>ignorance I pipe up with "both". I say I believe both due to the fact my
>TR4 has positive ground and other cars have negative ground. Therefore
>electricity must flow in either direction. My instructor is taken off guard
>by this, and throws out a "top of his head" explanation. If I understood
>correctly he surmised that in fact the current flowed backwards and
>essentially the whole car was "live". I'm not buying it. What is the real
>nature of a positive ground system?
A good answer to dubious question. Alternatively you could have asked him
what he meant by "electricity" (and "flow").
The simple answer is that electicity flows from positive to negative. This
was a simple and arbitrary convention that was agreed about two centuries
ago. Then the electron was discovered and was found to have a negative
charge.
Electricity flows in the form of electrons through conductors (wires) and
because they are negative they travel from the negative terminal of the
battery to the positive terminal.
It is probably confusing at this stage to consider the flow of electricity
in semiconductors (transistors, diodes/rectifiers) and inside batteries.
Earthing/grounding one side of the battery in cars is just a wiring
convenience. The chassis/frame/body is used to provide one of the two
conductors necessary for electricity to flow. The alternative would be to
provide two wires for each device from spark plugs to tail lights - the
wiring would just be much more complex and both conductors in a device
would have to be insulated from the frame.
The choice of positive or negative grounding is simply a matter of
convenience related, I believe, to manufacturing of negative cased
alternators.
Regards, Trevor Jordan
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