In the circuits  (a), if at t=0, circuit is closed, and then the potential difference across the ends of capacitor increases with time, as shown in diagram (graph b). This is called charging of capacitor.

This can be represented by equation (1):

This can be represented by equation (1):

Similarly the discharging circuit is shown in figure (c). Closing the key at t=0, the discharging starts. The potential difference V_C which was equal to E at t=0, decreases exponentially with time t, as shown in graph (d).

The above process is mathematically represented as,

‘RC’ is called as the “time constant of circuit”, its dimension is M⁰L⁰T¹. Time constant is that time of circuit, at which the value of V_C during charging becomes 67% of maximum value, or during discharging becomes 33% of maximum value.

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