1. The problem statement, all variables and given/known data An RL circuit has a 9.0 V battery and a 5.5 ohm resistor. When the switch is closed, the current in the circuit is observed to increase from 0 to 0.30 A in 0.17 s. A) What is the inductance? B) How long after the switch is closed does the current have the value 0.47 A? 2. Relevant equations τ = L/R EMF = L*I / t I = EMF / R *(1-e^-tR/L) 3. The attempt at a solution I don't know how to find a time constant, my text doesn't explain it, which makes me think that this question may not even use this equation. I can't get to part B without an answer to part A. By using the second equation I got L = 5.1, but that isn't correct.