This is the continuous flow of charge around a circuit. Current can be defined as the amount of charge which passes through a point over a given time.
Recall that current is one of the seven(7) fundamental quantities and is measured in amperes(A).
Current is thus given by the formula: $$ \begin{equation}\begin{aligned} current(I)=\frac{charge(Q)}{time(t)}\\ \end{aligned}\end{equation} $$ The ampere is therefore equivalent to 1 coulomb of charge passing a certain point in a circuit in 1 second: $$ \begin{equation}\begin{aligned} 1\ A=\frac{1\ C}{1\ s}=1\ Cs^{-1}\\ \end{aligned}\end{equation} $$ The formula is often rewritten to make charge the subject of the formula. This is particularly useful in electrochemistry to determine the amount of charge required to preferentially discharge a certain mass: $$ \begin{equation}\begin{aligned} Q=It\\ \end{aligned}\end{equation} $$
If no charge is transferred from one point to another ($Q=0$) then no current is flowing ($I=0$) and vice versa.
Thus there can be a net positive or net negative charge present but if the charge does not flow then we cannot say that a current is present.
Mission details
- Find the amount of charge if a current of $3\ A$ passes for a time interval of $1\ minute$.
- What current is present if a charge of $4\ Faradays$ is flowing for $4\ s$. ($1\ Faraday\approx 96500\ C$)
Be sure to use SI Units!!
Conductors and insulators
- Conductors are materials which allow charge to easily flow
- Metals are good examples of conductors
- Insulators are materials which do not allow charge to flow readily
- Notice how the materials which are good insulators can be used to generate static electricity
- Hence, a material being a bad conductor does not disqualify it from being useful in studying and utilizing electricity
- Conductors can be charged by induction but they require an external electric field to be present and this external field can be generated by electrifying insulators by friction
- Conductors have atoms with loosely bound electrons which can freely move among atoms whereas insulators have atoms where the electrons cannot freely move among atoms
Electron flow and conventional current
We consider electron flow to be opposite in direction to conventional current. Electrons flow from the negative terminal of the battery to the positive terminal. The current on the other hand flows from positive to negative (high electric potential to low electric potential).