In electrostatic we have learned that any free positive charge will move from a high potential region to low potential region , while negative charges moves in the opposite direction.such a motion of charges along a specific direction constitutes an electric current.
Electric Current strength
The electric current or electric current intensity is defined as the rate of flow of electric charges. i=q\t.
In SI system electric current intensity is a quantity and its unit is ampere (A).
Conventionally the direction of current is fixed as the direction of flow of positive charges, however in metallic conductors flow of electrons constitute the current. The direction opposite to the direction of flow of electrons in taken as the direction of current . Though current has a direction , it is a scalar quantity as it does not obey laws in vector algebra.
Electric Current Density
In practise we have to use conductors of varying cross section and hence a more convenient way of expressing strenght of current is in a vector form "Electric current density Vector" . The magnitude of electric current density is defined as the electric current intensity per unit area j=i/a'
Source of Electro Motive force
The Device or arrangement which is able to to supply a continuous potential difference is called source of electro motive force
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