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Potential difference of an emf with internal resistance

  1. Jun 11, 2017 #1
    1. The problem statement, all variables and given/known data
    A battery of emf 2V and internal resistance 0.1ohm is being charged with a current of 5 ampere.
    In what direction will the current flow inside the battery?What is the potential difference between the two terminals of the battery?

    2. Relevant equations
    If a battery of emf E and an internal resistance r has a current i flowing through it,potential difference across it's terminals,say V is defined as:
    V=E-ir

    3. The attempt at a solution
    When we connect a battery in a circuit,INSIDE THE BATTERY,current flows from the negative terminal to the positive terminal,which discharges the battery(correct me if I'm wrong here plz)
    So,while recharging,the direction should be reversed,shouldn't it?
    Also,the formula stated above,yields the answer to be 1.5V
    But,the answer given is:
    Current flows from the anode to the cathode
    V.d=2.5 Volts
    I am guessing if I just get the reasoning for the first part,the formula stated could be modifed to yield the correct answer,but why does the current inside the battery flow from the negative terminal to the positive terminal,wouldn't that discharge the battery?
     
  2. jcsd
  3. Jun 11, 2017 #2

    gneill

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    Staff: Mentor

    Conventional current (movement of positive charges) flows from the positive terminal, though the external circuit, and back to the negative terminal of the battery. Internal to the battery, conventional current is "pumped" from its negative terminal to its positive terminal. When analyzing circuits it's in your best interests to express things in terms of conventional current as that is the accepted standard and less likely to cause confusion amongst those reading your equations and explanations.
    Correct.
    You don't need to modify the formula, just get the current direction correct. That means assigning the appropriate sign to the current value to reflect its direction with respect to the direction assumed for the current definition in place when the formula in question was written.
     
  4. Jun 11, 2017 #3
    Ok,I got that.
    Now,if I am correct and the direction does get reversed,doesn't that mean that conventional current is moving from the positive to the negative terminal now?
    But,as I stated in the post,the answer given is:current flows from anode to cathode.
     
  5. Jun 11, 2017 #4

    gneill

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    Staff: Mentor

    The terms "anode" and "cathode" can sometimes be tricky to interpret when a device is not being used in its normal operating mode. For a battery that is driving current into a circuit the positive terminal is designated as the cathode. If the battery is being charged and current is thus flowing into its positive terminal, that terminal is then referred to as the anode.

    Take a look at the Wikipedia article:
    https://en.wikipedia.org/wiki/Anode
     
  6. Jun 12, 2017 #5
    Ok,got it.Crystal clear now,thanks!
     
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