The flow of charged particles (typically electrons) in a conductor due to an external force (potential difference). The flow of electric current is shown in Fig.

There are two methods of current flow introduced: a conventional method and a standard method. The conventional method was established in the 18th century before the full understanding of electricity. Conventional current flow represents the direction of charges from higher potential (typically positive) to lower potential (typically negative), whereas the standardized flow is quite opposite to conventional flow as the charges are negatively charged; it tries to repel from the negative side and move forward towards the positive side.

5.1:Measurement of current

Electric current is defined as the passage of charge in a certain direction. It is denoted by ampheres (A).It is measured in time ratio of electric charge through the conductor. If q is the charge flowing through any cross section of the conductor in time t ,then,

Electric current, I=q/t

5.2: Electric Charge

The SI unit of electric charge is coulomb (C). It represents the total amount of electric that flows through a conductor in one second when a constant current of one ampere (A) is maintained.

Imagine a tiny particle of electron that carries electric charge, and the quantity of electric charge with the number of electrons is represented by coulomb (C). The coulomb tells you how much total charge has flowed through a point in the circuit for a specific duration.

Imagine water flowing through the water pipe, and the amount of water flowing through at a particular point is calculated in liters; similarly, the amount of charge flowing at a particular point is measured by coulomb.

A single electron carries e ≈ -1.602 x 10^-19 amount of charge and this charge is negative having a specific value denoted by symbol “e”.

The relationship between coulomb , electron , and elementary charge is represented as,

1C = number of electrons * e ( i.e -1.602 x 10^-19 C/electron)

Then, if want to calculate how many number of electrons are consists in one coulomb is represented as,

Number of electrons=1C/e =1C/(-1.602 x 10^-19 C/electron)

= 1/-1.602 x 10^-19

Approximately ≈ 6.2415 x 10¹⁸ electrons.

As you seen earlier the electric current,

I=q/t

From above equation, Q=I/t

5.3 : Coulombs law

The Coulombs law states that the magnitude of electrostatic force is directly proportional to the product of the magnitudes of two different charges and inversely proportional to the square of the distance between them.

The mathematical Expression represented as ,

Where,

F= Magnitude force of electrostatic force

K= Proportional Constant

=8.99*10⁹

q₁,q₁=Magnitude of charges

r= Distance between the two charges

(Note: electric charge is vector quantity where it has both directions and magnitude).

5.4:Drift Velocity

When voltage is applied across the ends of a conductor, the free electrons start drifting towards the positive terminal of the source. The average velocity of a free electron when a voltage is applied is called drift velocity v_d. The free electrons of a drift velocity are relatively small, of the order of 10-5 ms-1.

Here everyone has a doubt that if the drift velocity is very small, how a light turns on very quickly when switched on? The answer is that when we apply the voltage to the conductor, the free electrons drift at the same time in every place at once.

5.5 Relation between Current and Drift Velocity

Examine a section of the wire where current I is flowing as indicated in fig. when voltage is applied.

Let A be the wire's X-section area.

n be its electron density, or the quantity of free electrons per unit volume

e be the charge on each electron

V_d bethe drift velocity of free electrons

As seen in the figure, all of the free electrons that are located vd to the right of the cross section at P will pass through it in a single second. This has nA vd passing the cross section at P per second.

Since A, n and e are constant, I ∝ vd

I ∝ V_d since A, n, and e are constants.

Because of this, the drift velocity of free electrons in a wire closely correlates with the current flowing through it.