1. The problem statement, all variables and given/known data If you have this RC Circuit (ignore the yellow path of current): http://i.imgur.com/Mi2bj.png When you are calculating time constant=RC, what would you use for R? R1=100 ohms, or Req=300 ohms 2. Relevant equations time constant = RC 3. The attempt at a solution I would think its just the 100 ohms, because initially, the current is only flowing through that resistor.