Current

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Current

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Current

The electron in the outermost orbit of an atom is referred to as valence electrons. When sufficient energy or external force is imparted to these electrons, it moves from a negatively charged atom to a positively charged atom. This flow of electrons is called current. The lower case or upper-case alphabet of I is used to represent current.

An electric current may be defined as the rate of motion of electric charge across a cross-sectional boundary. The unit of current is the ampere (A) named after the French physicist A.M. Ampere. One Ampere corresponds to the charge moving at the rate of one-coulomb per second (C/s).

The current is expressed as

$\tiny i=\frac{dq}{dt}\;C/s\;(A)$

The term ‘dq’ is the amount of charge that passes by in a time interval ‘dt’

Example:

If 0.5 Coulombs of charge flow in a conductor across a cross section in 2 sec, find the current through it.

$\bg_white \tiny I=\frac qt=\frac{0.5}2\;=\;0.25\;A$

Example:

How many electrons pass a fixed point on the conductor in 1 minute and 1 second if it carries a current of five amperes.

$i=\frac{dq}{dt}\;=\;5\;A\;=\;C/s\;=\;5*60\;=\;300\;C/min$

As one coulomb is equal to 6.24x1018 electrons, the number of electrons passing a fixed point on the conductor in one second and one minute is calculated as 3.12x1019 electrons per second and 1.872x1021 electrons per minute respectively.

Example:

Find the time taken by the one coulomb to cross a given point in the circuit which constitutes four amperes of current in the circuit.

$I\;=\;\frac qt\;A$

$t=\frac QI\;=\;\frac14\;=\;0.25\;s$

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