NEET Physics Notes Current Electricity-Electric Current
Electric Current
Electric Current
Electric current is defined as the time rate of flow of electric charge through a cross-section of the conductor. If a charge ∆t
passes through the area in time interval ∆q at uniform rate, then current I is defined as instantaneous value of current is given by
SI unit of electric current is Ampere (A).
- Conventional direction of flow of current is taken to be the direction of flow of positive charge or opposite to the direction of flow of negative charge.
- Electric current is a scalar as it does not follow the vector law of addition.
- If n-particles, each carrying a charge q, pass through a given cross-section in time t, then current
As an example, 1 A current is equivalent to flow of 6.25 x 1018 electron/s.
Current Density
Current per unit area is termed as current density.
Drift Velocity
Drift velocity is the average uniform velocity acquired by conduction electrons inside a metallic conductor on application of an external electric field.
The drift velocity is given by the relation
where, 
known as relaxation time, is the mean value of time between two successive collisions of an electron with ions in the conductor.
Drift velocity per unit electric field is called the mobility of the electrons. Thus, mobility
In terms of drift speed, electric current flowing through a conductor is expressed as
I =nAevd
where,
A = cross-section area of conductor,
n = number of conduction electrons per unit volume
vd = drift velocity of electrons
and e = charge of 1 electron.
Ohm’s Law
According to Ohm’s law, physical conditions (temperature, mechanical strain, etc.) remaining unchanged, the current flowing through a conductor is directly proportional to the potential difference across its ends.
Thus, 
where, R is a constant known as the electrical resistance of given conductor.