Discharging of a Capacitor

As shown in Figure given below, when S is shifted to b, C is discharged through R.

It will be seen that the discharging current flows in a direction opposite to that the charging current as shown in Figure given below:

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Hence, if the direction of the charging current is taken positive, then that of the discharging current will be taken as negative. To begin with, the discharge current is maximum but then decreases exponentially till it ceases when capacitor is fully discharged.

Since battery is cut of the circuit, therefore, by putting V = 0 in the following equation

of Article – Charging of Capacitor, we get

At the start of discharge, when t = 0, v_c = V

∴ log_eV = 0 + K ;

log_eV = K
Putting this value above, we get

It can be proved that

V_R = − Ve^−t/λ

The fall of capacitor potential and its discharging current are shown in Figure (b).

control circuits where a square-wave input is applied across an R-C circuit as shown in Figure (a) given below. The different waveforms of the current and voltages are shown in Figure (b), (c), (d), (e) in the above image. The sharp voltage pulses of V_R are used for control circuits.