If a resistor and capacitor are wired into a series circuit and the capacitor is charged, it to become fully charged by a battery with emf of takes a certain amount of time for the capacitor on the capacitor e. the time it takes for the voltage to reach 0.632 of its maximum value is called the time constant, t for the combination. when the capacitor discharges, the time it takes for the voltage across the capacitor to reach 0.368 of its maximum value is also the time constant. the time constant depends on the value of the net resistance (r is in ohms) and net capacitance (c is in farads) in the combination t = rc to determine the time constant when charging, you must apply kirchoffs rules to the circuit. following the loop, your equation should be: e-ri c _ it can be shown that the solution to this equation in terms of the potential difference across the capacitor is ve)e(-e) when discharging, at time t = os, the charge on the capacitor is q(0) - ce. with kirchhoff's loop equation, we find that: i_ri = 0 c the solution to this equation in terms of the potential difference across the capacitor is: v(t) = ee exponential fit to you determine the time constant and other quantities within the lab. for the discharging circuit, you will use y = a*exp(-c*x )+ b to fit the graph. for the charging circuit, you will use y a*(1 - exp(-c*x) + b. notice that the "c" loggerpro wl use an used in the curve fit is not the same as the "c" used to stand for capacitance.