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### 5.3 Current of Electricity

In this section we'll discuss the notion of electricity.

The electric current is the rate of flow charged particles. It's SI unit is ampere(A).
$$I=\frac{Q}{t}$$
where,$I=$ Current, in $'A'$
$Q=$ total charge passing a point, in $'C'$
$t=$ time for charge to flow across the point, in $'s'$

From this definition, we can also find the expressions in different forms for a current in the wire in terms of individual charges. We can almost approximately visualize the flowing electrons in the wire as the figure below,

Then the expression for the current in the wire is given by,$$I=nqv$$
where,
$I=$ Current, in $'A'$
$q=$ charge of individual electrons, in $'C'$
$v=$ drift velocity of the electrons, in '$ms^{-1}$'
$n=$ Charge density (charge per unit length), in '$Cm^{-1}$'

Convention on the flow of the current

The case we are interested(in particular the flow of charge in metal) has the direction of current flow from negative terminal to the positive terminal, i.e. (negative charge flow). However, due to historical reasons, the convention of the the current is taken to be the flow of the positive charge(i.e. from Positive terminal to the Negative terminal). The direction of convention is as shown in the diagram below,

Here's an introduction to current,