Electric current:

The movement of electric charge is called as an electric current, the intensity of which is generally measured in amperes. Current can consist of any moving charged particles; mostly these are electrons, but any charge in motion constitutes a current. Electric current is the rate of charge flow past a given point in the electric circuit, measured in Coulombs/second which is termed as Amperes. The process by which the electric current passes through the material is termed as electrical conduction, and the nature of it varies with that of the charged particles and the material through which they are travelling.

While the particles themselves can move quite slowly, sometimes having average drift velocity only fractions of a millimeter per second, the electric field which drives them itself propagates at close to the speed of light, enabling electrical signals to pass quickly along wires.

 In most of the DC electric circuits, it can be assumed that the resistance to current flow is a constant so that the current in circuit is related to voltage and resistance by Ohm's law.

This flowing electric charge is carried by moving electrons, in a conductor such as wire; in an electrolyte, it is instead carried by ions, and, in plasma, by both. The SI unit for measuring rate of the flow of electric charge is ampere. The electric current is measured by using an ammeter.

Current density is the measure of density of the electric current. It can be defined as a vector whose magnitude is the electric current per cross-sectional area. In SI units, current density can be measured in amperes per square meter. I=J.A where I is current in conductor, J is current density, and A is cross-sectional area. The dot product of 2 vector quantity signifies that electric current is a scalar. Electric currents in solids typically flow slowly. Any accelerating electric charge, and thus any changing electric current, gives rise to an electromagnetic wave which propagates at very high speed outside the surface of the conductor. The ratio of the speed of the electromagnetic wave to the speed of light in free space is called as velocity factor, and depends on electromagnetic properties of the conductor and the insulating materials surrounding it, and on their shape and size.

The nature of these 3 velocities is illustrated by an analogy with the 3 similar velocities associated with gases. The low drift velocity of charge carriers is analogous to air motion; or in other words, winds. The high speed of the electromagnetic waves is analogous to the speed of sound in a gas; whereas the random motion of charges is analogous to heat - the thermal velocity of the randomly vibrating gas particles.