Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

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

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

share|improve this question

closed as off-topic by Emilio Pisanty, tpg2114, Dimensio1n0, Waffle's Crazy Peanut, Qmechanic Nov 6 '13 at 12:16

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – Emilio Pisanty, tpg2114, Dimensio1n0, Waffle's Crazy Peanut, Qmechanic
If this question can be reworded to fit the rules in the help center, please edit the question.

    
Refer to Lenz's Law: Induced current has a direction such that its magnetic field opposes the change in magnetic field induced in the current. –  Signus Sep 24 '13 at 20:06
    
@Signus and so..? –  sunrise Sep 24 '13 at 20:07
    
@Signus I think that the correct expression is the second, because the self inducted emf opposes to the inducted emf.. do you agree? –  sunrise Sep 24 '13 at 20:12
    
I do believe the second equation is correct as the self-inductance does oppose the induced current already on the wire/coil. That is why I mentioned Lenz's Law. I always think to myself "induction is always in the opposite direction of what my brain thinks." –  Signus Sep 24 '13 at 20:25
1  
Doesn't the term $-LdI/dt$ already account for the induced EMF $E$ so there must be only one of these in the equation? –  Satwik Pasani Sep 25 '13 at 1:25