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Signs of emf inducted and autoinducted

  1. Sep 24, 2013 #1
    1. The problem statement, all variables and given/known data
    I'm a little confused.. When I write the equation of the circuit, do I have to keep the signs of the induced emf and self-inductance opposite?

    I'll try to explain better my doubt:
    Consider a coil that has resistance R and inductance L. Running a current will give rise to both an induced emf and self-inductance, and the situation is:

    induced emf= -k

    self-inductance= [itex]-L \frac{dI}{dt}[/itex]

    Now, my question is: the equation of the circuit is given by:

    [itex]-k -L \frac{dI}{dt}=RI[/itex]

    or by

    [itex]k -L \frac{dI}{dt}=RI[/itex] ?

    3. The attempt at a solution
    I think that the self-inducted emf fights the inducted emf so, self-inducted emf and inducted emf have ho have different signs and so the equation of the circuit is given by
    [itex]k -L \frac{dI}{dt}=RI[/itex]. But I'm not sure. Could you help me?
  2. jcsd
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