What is a capacitor? Explain capacitance and give its $SI$ unit.

(N/A) capacitor is a system of two conductors separated by an insulator.
Definition: An arrangement in which two good conductors of arbitrary shape and volume are arranged close to one another,but separated from each other,is called a capacitor.
Suppose the conductors have charges $Q_1$ and $Q_2$ and potentials $V_1$ and $V_2$. The potential difference is $V = V_1 - V_2$.
$A$ single conductor can be used as a capacitor by assuming the other at infinity.
The conductors may be charged by connecting them to the two terminals of a battery.
$Q$ is called the charge of the capacitor,though this in fact is the charge (magnitude) on one of the conductors. The total charge of the capacitor is zero.
The electric field $\vec{E}$ in the capacitor is from $+Q$ charge to $-Q$ charge and it is proportional to the charge $Q$. Therefore,$E \propto Q$.
The potential difference $V$ is the work done per unit positive charge in taking a small test charge from conductor $2$ to $1$ against the field. Hence,$V$ is also proportional to the charge $Q$. Therefore,$V \propto Q$.
Hence,the ratio $\frac{Q}{V}$ is constant.
Therefore,$C = \frac{Q}{V} \quad (1)$
Here,$C$ is the capacitance of the capacitor.
Definition of Capacitance: The ratio of the amount of charge on the plate of a capacitor and the potential difference between the two plates is known as the capacitance of the capacitor.
The $SI$ unit of capacitance is the farad $(F)$.
Capacitance is independent of $Q$ or $V$.