By giving explanation of electric current, define current and its SI unit.

Explanation

`rArr` Due to motion of charges in conductor electric current is formed.
In a cross-section of a conductor let charge q + flows in time t in forward direction (in direction of electric field and q - charge flows in backward direction in the similar time t.
`rArr ` Net charge flowing in forward direction in given cross-section in time t,
q = q + - q -
`rArr` Electric current (Definition) : Net flow of charge through cross-section of a conduction in un time is called electric current (I).
`rArr ` When flow of charge changes with time, the electric current is defined as follows :
`rArr` ln time interval between t and t `Delta`t let nc charge flowing through cross-section conductor be `Delta`Q , then average current,
`rArr " " lt I gt = (Delta Q)`
by taking `underset(Delta t rarr 0)(" lim ")` we get instantaneous current ,
`I = underset(Delta t rarr 0 )( " lim ") (Delta Q)/(Delta t) = (d Q)/(dt)`
`therefore I = (dQ)/(dt)`
`rArr` Conventional current is taken in direction o motion of positive charge. In conductor positivt charge do not flow. Current is produced due to motion of electron. Hence, direction of current taken in opposite direction of motion of electron
`rArr` From I = `(q)/(t)` unit of electric current will be `("Coulomb")/("Second")`.
`rArr` In SI system unit of current is Ampere.
`rArr ` Definition of unit of electric current :
If in a cross-section of a conductor charge flowing in 1 second is 1 Coulomb `(6.25 xx 10^(18) "elelctron")` then current flowing through is called 1 Ampere.
value of electric current in devices used in day to day life is of order of ampere. Current flowing in lightening is oder of ten thousand ampere, current flowing in nerves of our body is order of `mu` A (microapmere).