Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Is 100 J of electric potential energy actually greater than -100 J of electric potential energy?

  1. Nov 30, 2018 #1
    Is the 100 J of electric potential energy actually greater than -100 J of electric potential energy?
     
  2. jcsd
  3. Nov 30, 2018 #2

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    They have the same magnitude but the sign is the indication of the work done (energy needed) to bring a +1C of charge from an infinite distance to points with those two potentials. The definition is that Positive work is needed to bring +1C to the +110J point (pushing up a hill) but negative work is done (i.e. energy is got out) then the +1C is brought to the -100J point (sliding down to a valley).
     
  4. Nov 30, 2018 #3

    jbriggs444

    User Avatar
    Science Advisor

    Given the way the question is phrased and the units that are used, I would interpret it to be about the potential energy of two configurations of the same system. One with a potential energy 100 J more than an arbitrary reference potential and one with 100 J less than the arbitrary reference.

    Clearly, one has 200 J less electrical potential energy than the other.
     
  5. Nov 30, 2018 #4

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Sounds fair and I can't find fault with that. The question could either require a totally theoretical answer or something practical. We would need the OP to give us a bit of help with the context. What does he actually want to know and why?
    Can @rpthomps help us to help him more, please?
     
  6. Nov 30, 2018 #5

    jbriggs444

    User Avatar
    Science Advisor

    Or it might have the syntax of a question but be devoid of semantics.
     
  7. Dec 3, 2018 #6
    Thanks guys for the response! The question, was answered, as intended by @sophiecentaur but @jbriggs444 brought up another way of thinking about it.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted