ELECTRIC CURRENT: Electric current is a quantity of electric charge, i.e, electrons flow through a point of an electric circuit per unit of time.

In a conductor any movement of electrically charged particles with respect to time is called electric current. It is nothing but the free electrons movement in a conductor to one direction.

The unit of electric charge(electron) is Coulomb and the unit of time is second. Then the unit of current is Coulomb/second, known as Ampere.

1 amp = 1 coulomb/1 second.
If Q coulomb charge flows through a electric circuit in t second, then current I = Q/t coulomb/sec or Ampere, which is S.I unit of current.

Suppose in a conductor electrons flow from left to right with the effect from externally applied electric field, conventional current flows from right to left, the opposite direction of electron flow.

TYPES OF CURRENT: There are two different types of current. 1) Direct current abbreviated as D.C. and 2) alternating current as A.C.
DIRECT CURRENT: It means unidirectional current, that is, when the motion of electric charge is unidirectional means,current does not change its direction periodically, is called direct current. The value is assumed constant with time.

Most common D.C source are battery.
ALTERNATING CURRENT: When the motion of electric charge is periodically change, i.e, current changes its direction from forward to backward and vice versa in several times per second is known as alternating current.

A.C current is cyclic in nature, current flowing positive direction in one half the cycle and negative direction in the other half. The current wave shape is sinusoidal.
Most common a.c source are alternator.