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Homework Help: Internal Resistance Graph

  1. May 19, 2009 #1
    When taking internal resistance into account, voltage/current graph has negative gradient (i.e. internal resistance).?

    My thoughts...

    Because for ohmic resistors, graph has a positive gradient. Why does one say that when V=0, Current = max, whilst the other says that when V=0, Current = 0?
  2. jcsd
  3. May 19, 2009 #2


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    Homework Helper

    Last edited by a moderator: Apr 24, 2017
  4. May 20, 2009 #3
    My question was answered in that thread, this is the result I got.

    [itex] E = I(R+r) [/itex] where R is the total resistance in the circuit and r is the internal resistance of the cell or battery. From this we can see that,

    [itex] E = V + Ir [/itex]


    [itex] V = E - Ir[/itex]

    When plotting a graph of potential different against current it is clear that the current I has a negative co-efficient: -r. Hence -r is the gradient of the line, and E is the y intercept. y=mx +c (remember?) this is just V=-rI+E.
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