1. The problem statement, all variables and given/known data Maximum current: I max = 4.62 * 10^-4 A Time constant of circuit: T = 3.9 seconds 2. Relevant equations T= RC 3. The attempt at a solution I'm trying to find the current after 1 time constant. Seems simple enough, the current changes by 63%. So (Imax)-(Imax * 0.63) or basically I max * 0.37 But the teacher just took I max * 0.63 !!! I thought it CHANGES by 63% not simply 63% of the original value!! I looked it up and all websites agree that the current after 1 time constant will be 0.37 of it's maximum value, hence a change of 63%! http://www.electronics-tutorials.ws/rc/rc_1.html Has the teacher made a mistake? I have deeply confused myself over a simple thought. Please help.