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Signal Ground and ground in general

  1. Aug 20, 2015 #1
    Hello Forum,

    If we connect one of the terminals of an AC voltage source to ground, the earthed terminal will maintain the same electric potential as planet earth. Earth can be assumed to be a huge spherical conductor whose electric potential does not change (much) when connected to a time-varying source: the little positive or negative charge it acquires does not change things much...
    so the terminal connected to ground will remain at that stable earth potential (which we arbitrarily call zero-volt potential) while the other AC source terminal change electric potential (larger than zero, smaller than zero) in reference to to grounded terminal...

    If we did not ground either terminals of the AC source, the potential difference would still be there but we would not know the instantaneous electric potential of either terminals. All we would know is that their difference is oscillating in time sinusoidally.

    Do I understand things correctly?

  2. jcsd
  3. Aug 20, 2015 #2


    Staff: Mentor

    Yes, you have it right. Think of an AC voltage on a spaceship for example.

    But, you are trying to think of potential as an absolute. It is more correct to think of potential difference. Voltage is always the potential difference between two points, just as distance is always between two points. We need a ruler with two ends to measure distance. Likewise, we need a voltmeter with two wire leads to measure voltage.

    Does that make sense to you?
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