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Calculating electrical energy over time

  1. Apr 12, 2013 #1
    Hello,

    Let's say I am generating 5 amp at a constant 1 volt and storing it in a battery without any loss of energy. The question is what am I adding to the battery? Am I adding power as a function of time or is it something else? So say if I were to calculate how much energy has accumulated after 5 hours how would I do that?

    Thank you.
     
    Last edited: Apr 12, 2013
  2. jcsd
  3. Apr 12, 2013 #2

    russ_watters

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    Staff: Mentor

    P=VI
    E=PT

    Power is energy added per unit time.
     
  4. Apr 13, 2013 #3
    Ah I see, thank you.
     
  5. Apr 13, 2013 #4
    Amp means coulomb per second. Volt means Joule per coulomb.
    therefor V x I means Joules per second = power.
    power x time = energy in Joules
     
  6. Apr 13, 2013 #5
    What if my voltage isn't constant? Doesn't that mean that my power isn't constant either? And doesn't E=PT rely on constant power?
     
  7. Apr 13, 2013 #6
    you would then find yourself talking about 'instantaneous power'. If the voltage changes presumably the current also changes.
    An interesting example is in AC circuits where V and I are changing and can be out of step.
     
  8. Apr 13, 2013 #7
    what do you mean by instantaneous power? Wait do you mean to take the integral of the power function with respect to time?
     
  9. Apr 13, 2013 #8
    Sure.

    You're right again. [itex]E(t) = \int_{t0}^t P(\tau) \mathrm{d}\tau[/itex] is true in general.
     
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