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Electric field lines between 20/30 V point charges vs. 10/0 V

  1. Jul 13, 2013 #1
    1. The problem statement, all variables and given/known data

    What would the electric field lines / equipotential lines look like between point charges that are set up with potentials of 20 volts and 30 volts versus point charges that are set up with potentials of 0 volts and 10 volts?

    3. The attempt at a solution

    At first I thought the electric field lines would look different, but the more I thought about it, the more it seemed like they would be the same, since only the difference in V counts as opposed to the "absolute" values of V. Is this correct? Thank you all so much!

    Added question: I completely forgot about this, but would the lines extend from the 10 V charge toward the 0 V? I know the lines go from the positive charge from the negative charge, so I'm pretty sure they would go from the higher V to the lower V, but I just wanted to make sure. Thank you!
     
  2. jcsd
  3. Jul 13, 2013 #2

    BruceW

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    It is true that only difference of voltage is important but remember the convention about voltage at infinitely far away. This is important for this problem.
     
  4. Jul 16, 2013 #3
    Thank you so much!
     
  5. Jul 16, 2013 #4

    BruceW

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    hehe. no problem!
     
  6. Jul 17, 2013 #5
    What is a point charge set up with a potential of 20 V ? :confused:

    Since the potential due to a point charge is

    [tex] \frac {1}{4 \pi \epsilon_0} \frac {Q}{r} [/tex]

    the potential near a point charge will become infinite for any non-zero charge.
    If the point charge is merely a very small sphere, you still need to know the radius to get the charge from the potential.
     
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