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Homework Help: What the! isn't this plug and chug?

  1. Oct 26, 2005 #1
    A car battery with a 12 V emf and an internal resistance of 0.050 is being charged with a current of 60 A.

    (a) What is the potential difference V across its terminals?

    Okay i have an equation that should work perfectly!!
    Points a and b are located at he terminals of the battery, thus the potential difference Vb-Va is the termian to terminal potential difference V across the battery, we see that:
    V = EMF - ir. r is the internal resitance of the battery, and they give me 60 amps as the current?
    V = (12V)-(60A)(.050) = 9V, which is wrong!
  2. jcsd
  3. Oct 26, 2005 #2
    You are CHARGING the battery, not discharging the battery, so there is no way the resulting voltage would be lower than the nominal voltage...
  4. Oct 27, 2005 #3
    I looked in the book and it gives me no case if ur charging the battery, whats the difference? It also didn't say that the formula i used is only for discharging a battery
  5. Oct 27, 2005 #4
    A simple change in sign of the term "ir" maybe??
  6. Oct 27, 2005 #5
    Ohhh!! thanks again bigman!! :biggrin:
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