1. The problem statement, all variables and given/known data An inductor has a current I(t) = (0.480 A) cos[(280 s-1)t] flowing through it. If the maximum emf across the inductor is equal to 0.490 V, what is the self-inductance of the inductor? 2. Relevant equations ε = -L*di/dt 3. The attempt at a solution I would have that this would be as easy as using the above equation, and taking a derivative as necessary. The one thing that throws me is the value of t and the fact that it is unknown. So, what I did was, ε = LdI(t)/dt Taking the derivative of I(t), I get dI(t)/dt = -(.48)(1/280)sin(1/280*t) If I even did that correctly, I still don't have a value of t in order to solve for L. I know that the maximum emf across the inductor will occur right at t=0, right? As the current reaches a steady value, dI/dt goes to 0, at which point the inductor acts as a wire and there is no emf across it. But if that's the case, and this max emf of .49 V occurs at t=0, then sin(0) = 0, and L = 0. I think I'm completely missing something, here. Any help in the right direction would be great. Thanks!