What is electricity and define electricity

-: Electric Current 

1. electric current  (i)

-: We know that electric potential ofa body is defined as the degree of electrification and it determines the directios of flow of charge. Consider two bodies 'A' and 'B' charged to potentials 'V1'and 'V2' , respectively,  such that V1 > V2 . 

-: If they are not connected to each other  (fig.1 ), no charge flows and hence their potentials remain constant. 

(Fig.1)

-:If they are connected by means of good conducter R, positive charge flows from higher potential to the lower potential or negative charge,  i.e., electrons move from lower potential to higher potential till the potentials become equal. This is an instantaneous process .

Current strength,  in a conducter,  is defined as the rate of flow of charge across any cross-section of the conducter. 

If a charge 'q' flows across any cross-section in 't' second,  current i is given by -: 

i = q/t

The above formula holds good if the flow of charge is uniform with time.  In case of non-uniform flow, let ♢q be the small amount of charge flowing across any cross-section of the conducter in a small interval of time ♢t, then current i is given by 

i=♢q/♢t

Electric current is time derivative of charge 

Unit of current in S.I is coulomb/sec. or ampere.

-: Type of electric currents

1. Steady current - 

A current is said to be steady if its magnitude is constant and direction is always the same. (Fig4.1 i ) shows the current -time graph for such a current.

2. Variable current - 

A variable current, in general,  is defined as the current which changes in magnitude with time while its direction may or may not change. ( fig4.2 ii) shows a current whose magnitude changes within 1A and 3A, while its direction is always same.  Such a current is called variable direct current. (fig4.2 ii).

-: Unit of Electric Current 

(i) C.G.S. electrostatic unit  (esu)-

 The current flowing through a conducter is said to be one esu if a charge of 1 esu flows across any of its cross-section in one second.
1 esu of current = 1 esu of charge / 1 second
The esu of current is called statampere.

(ii) S.I. unit -

The current flowing through a conducter is said to be 1 ampere if a charge of 1 coulomb flows across any of its cross-section in one second. 

1 ampere = 1 coulomb /1 second.

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