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Battery loaded down ?

  1. Dec 10, 2012 #1
    Battery "loaded down"?

    1. The problem statement, all variables and given/known data

    A current of 20 amperes is being drawn from a battery whose emf is 24 volts. The
    internal resistance of the battery is 0.3 ohms. By how many volts is the battery "loaded
    down"?


    2. Relevant equations

    V = IR

    3. The attempt at a solution I dont know what it means for the battery to be loaded down? Try searching for it but could not find anything. Please advice.
     
  2. jcsd
  3. Dec 10, 2012 #2

    gneill

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    Staff: Mentor

    Re: Battery "loaded down"?

    Granted, "loaded down" is an inexact (perhaps colloquial) expression. In this case it refers to the amount by which the emf presented at the battery's terminals has fallen below its rated value.
     
  4. Dec 10, 2012 #3
    Re: Battery "loaded down"?

    Oh so after a battery has been used?
     
  5. Dec 10, 2012 #4

    gneill

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    Re: Battery "loaded down"?

    No, while it is being used.
     
  6. Dec 10, 2012 #5
    Re: Battery "loaded down"?

    Okay, I'm still unsure of how to solve this but I understand what you are saying so far, i think.
     
  7. Dec 10, 2012 #6

    Dick

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    Re: Battery "loaded down"?

    I'm kind of curious here. How much the emf at the terminals is below the rated value depends on what load you put on the battery right? So the "loaded down" voltage will be a function of the load resistance, right? Not a single number?
     
  8. Dec 10, 2012 #7

    gneill

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    Re: Battery "loaded down"?

    Indeed. Which is why the question asks, 'By how many volts is the battery "loaded
    down"?' given a load drawing 20 A.
     
    Last edited: Dec 10, 2012
  9. Dec 10, 2012 #8

    gneill

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    Re: Battery "loaded down"?

    You have a 24V ideal voltage supply in series with 0.3 Ohms inside a box labelled "24V Battery". If a load that draws 20A is connected to this battery, what voltage will you "see" at the battery's terminals?
     
  10. Dec 10, 2012 #9

    Curious3141

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    Re: Battery "loaded down"?

    Is it necessary to calculate that? If "load down" refers to the amount by which the "usable" voltage has fallen, then they don't even need to provide the EMF of the cell, right? (given that they already stated the internal resistance and the current drawn)
     
  11. Dec 10, 2012 #10

    Dick

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    Re: Battery "loaded down"?

    Ooops. I missed that they gave you the current. Duh. Sorry. Carry on.
     
  12. Dec 10, 2012 #11

    gneill

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    Re: Battery "loaded down"?

    How one gets to the answer depends upon one's understanding of the concepts. What is obvious to one may require a bit of "a-hah!" for another, particularly if it's early days studying a subject.

    To answer your question, yes, you can determine the potential drop given the load current and the internal resistance. Whether or not this will be obvious or useful to the initial poster is another question :smile: Perhaps a_patel32 can comment.
     
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