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Subject: Re: Old easy question?

Date: 01/31/02 at 12:45 PM
Posted by: tom
E-mail: tom@dlsengineering.com
Message Posted:

In Reply to: Re: Old easy question? posted by Mike on 01/30/02 at 9:41 AM:

Ground DOES NOT act as a supply. If you think about it, ground is finite. Therefore if electrons constantly flowed into it, eventually it would run out of room. Conversly if they constantly flowed out of it, it would run out of electrons. However, ground can be thought of as a conductor, that is something that allows current to flow through it(a path for current flow). In what we are talking about now, ground is allways used as a reference to provide a baseline, a reference point from which we can measure the polarity and magnitude of somethings potential. What determines somethings potential with respect to ground is the source of power, be it a generator, power supply, battery, etc.. Think of it this way, if we had two batteries and connected the positive terminal of one to ground and the negative terminal of the other to ground, the negative terminal of the battery who's positive terminal was connected to ground would be negative with respect to ground. Conversly, the other batteries positive terminal would be positive with respect to ground. Now if we connected two loads, one between ground and one of the battery terminals not connected to ground and the other load between ground and the other non grounded terminal, current would flow from ground to the load in one of them and in the other current would flow from the load to ground. I hope I made a little more sense this time. Also, you are right as far as how fast electrons move. They do not move at the speed of light. A matter of fact, they dont move anywhere near the speed of light, they only move a few meters per second. What does "move" at about the speed of light is the effect of current flow. To elborate a little more on what john said, if you took 100 pool balls and lined them up from 1 to a 100 then hit the 1 ball with a force moving only a few inches per second, none of the balls would move at a greater speed then that force. However the effect of the force would be felt at the 100th ball at a very small instance of time from the impact on the 1st ball. Therefore, the effect of this force would travel at a much higher velocity then the movement of any single ball. This is simular to what happens with current flow. As one electron is moved from its orbit, another electron is moved into that orbit almost instantly, and so on. Thus any individual electron does not move very rapidly but the overall effect of their movement is felt allmost instantaniously. As far as a limit on how long a 60hz transmition line can be, frequency is not an issue at a low frequency such as 60hz. A factor that would have to be taken into consideration is impedance. What your talking about in your question is wavelength. Wavelenght does not matter at 60hz as far as transmition length. It does matter at much higher frequencies but thats a totaly different subject.


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