Capacitance (C) is calculated as the quotient of charge (q) by potential difference (V):
$C = \frac{q}{V}$
Nevertheless, capacitance is fundamentally dictated by the capacitor's physical construction, specifically its plate area, the spacing between plates, and the dielectric material. While charge (q) and potential difference (V) are proportional to capacitance, they do not define it. A capacitor, based on its inherent geometry, possesses a constant capacitance value.
A circuit consisting of a capacitor C, a resistor of resistance R and an ideal battery of emf V, as shown in figure is known as RC series circuit. 
As soon as the circuit is completed by closing key S₁ (keeping S₂ open) charges begin to flow between the capacitor plates and the battery terminals. The charge on the capacitor increases and consequently the potential difference Vc (= q/C) across the capacitor also increases with time. When this potential difference equals the potential difference across the battery, the capacitor is fully charged (Q = VC). During this process of charging, the charge q on the capacitor changes with time t as
\(q = Q[1 - e^{-t/RC}]\)
The charging current can be obtained by differentiating it and using
\(\frac{d}{dx} (e^{mx}) = me^{mx}\)
Consider the case when R = 20 kΩ, C = 500 μF and V = 10 V.