1. The problem statement, all variables and given/known data After a long time, an inductor is disconnected quickly from the battery and then attatched to a resistor. 2. Relevant equations V = Ldi/dt V = ir 3. The attempt at a solution KVL: voltage across inductor - voltage across resistor = 0 Ldi/dt - ir = 0 di/i = rdt/L ln|i| from i(t) to i(0) = rt/L + C i(t)/i(0) = e(rt/L +C) i(t) = i(0)Cert/L At time t= 0, i(t) = initial current i(0). Plugging in i(t) = i(0) and t = 0 gives C =1. Now we have i(t) = i(0)ert/L The correct equation is i(t) = i(0)e-rt/L, different from what I have; I have a positive time constant r/L. I know i(t) must be smaller than i(t) when time increases, and usually this is taken care of by a negative constant of integration, but as C = 1, the only way I can account for i(t) < i(0) is to use negative time. Derivations I have seen started off KVL with -Ldi/di - ir = 0, but I don't understand why my method doesn't also work. Is my method incorrect?