# Signs of emf inducted and autoinducted

1. Sep 24, 2013

### bznm

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= $-L \frac{dI}{dt}$

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

$-k -L \frac{dI}{dt}=RI$

or by

$k -L \frac{dI}{dt}=RI$ ?

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
$k -L \frac{dI}{dt}=RI$. But I'm not sure. Could you help me?