and the direction of conventional current point in opposite direction as shown in Figure . . Mathematically, a transfer of positive charge is the The electric current in a conductor is defined as the rate of flow of charges through a given cross-sectional area A. It is shown in the Figure .
. Figure . Charges flow across the area A If a net charge Q passes through any cross section of a conductor in time t, then the current is defined as I t . But charge flow is not always constant.
Hence current can more generally be defined as t avg = ∆ ∆ ( . ) Where ∆Q is the amount of charge that passes through the conductor at any cross section during the time interval ∆t. If the rate at which charge flows changes with time, the current also changes. The instantaneous current I is defined as the limit of the average current, as ∆ t ® t dQ dt t → lim ∆ ∆ ∆ ( .
) The SI unit of current is the ampere (A) s That is, 1A of current is equivalent to coulomb of charge passing through a perpendicular cross section in a conductor in one second. The electric current is a scalar quantity. 12th - 12th - - - - - Unit CURRENT ELECTRICITY electric field accelerates the electrons, while ions scatter the electrons and change their direction of motion. Thus, we see zigzag motion of electrons.
In addition to the zigzag motion due to the collisions, the electrons move slowly along the conductor in a direction opposite to that of E as shown in the Figure . . Ions Any material is made up of neutral atoms with equal number of electrons and protons. If the outermost electrons leave the atoms, they become free electrons and are responsible for electric current.
The atoms after losing their outer most electrons will have more positive charges and hence are called positive ions. These ions will not move freely within the material like the free electrons. Hence the