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I Rise in Voltage across a battery

  1. Mar 4, 2017 #1
    Let's say you have a circuit connected to a 15 volt battery. If current travels from the negative terminal of a 15 volt battery to the positive terminal, the voltage is said to rise 15 volts. I believe this is right, but correct me if I'm wrong. Assuming that is right, then does that mean that the electric potential at the negative terminal of the battery is zero volts and the electric potential at the positive end of the battery is 15 volts, because voltage is the difference in electric potential, so voltage = vf - vi = 15 V - 0 V = 15 volts. Am I correct in thinking this is the case? If so, can someone explain to me why the electric potential at the negative end of the battery is zero volts? Specifically can someone explain to me why the electric potential at the negative terminal of the battery is zero volts "REGARDLESS" of what else is in the circuit. So why is the negative terminal of the battery always zero volts in electric potential regardless if you have nothing but a wire in the circuit, 2 resistors, or 7 resistors, etc...? I could really use some help with this, conceptualizing why it's zero electric potential at the end of the circuit, regardless of what is in the circuit is killing me inside, because I can't grasp the concept. Thanks in advance.
  2. jcsd
  3. Mar 5, 2017 #2
    The short answer is, it doesn't matter. All that's important is the voltage difference--unless you connect the circuit to something else. As long as you keep the battery and its circuit in isolation you can call the terminal voltages anything you want, as long as the one is 15 V higher than the other. Picking one to be zero is often convenient. But if you connect the negative pole to ground you've connected it to something that is conventionally agreed to be zero, so then you have to call it zero itself. In practice, grounding the negative pole is probably conventional enough that people automatically call that voltage zero whether it's actually grounded or not.
  4. Mar 5, 2017 #3


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    You could also say the potential is -15 volts at the negative terminal and 0 at the positive. Or -7 at the negative and +8 at the positive. The only thing that matters is the difference between the terminals, not the absolute numbers, since absolute potential is impossible to measure.
  5. Mar 5, 2017 #4
    Yeah, the absolute offset of the voltages is irrelevant. As long as you do it to all parts of the circuit consistently, you can add/subtract any value you like.

    This gets interesting when you consider singular charges and their electric potential. As there is no particularly good spot to call 0V, often the "infinitely far away from the charge" is used as the 0V reference.
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