The current in some dc circuits decays according to the function i=i0e−t/τ, where i is the current at some point in time, i0 is the initial current at time t=0, and τ is the time constant determined by the properties of the circuit. if you start such a circuit with an initial current of 1.2 amps, and find that after 3.5 seconds have passed it has a current of 0.2 amps, what is the value of the time constant τ for this particular circuit?