What is electric charge? #### April 9, 2020

While studying electrical engineering, the engineer should be familiar with the first electrical engineering terms. The charge is also one of the first and fundamental building block units of electrical current. One can explain the charge definition in simple words as:

“Charge is an electrical property of the atomic particles of which matter consists. It is measure in coulombs (C)”

We study in our basic elementary science that all matters are composed of significant building blocks known as atoms. Every atom consists of electrons, protons, and neutrons. The charge on an electron is negative, that is equal to 1.602×10^-19 in magnitude. While the charge on a proton is the same but is positive in magnitude. The presence of both electrons and protons in similar numbers leaves an atom neutrally charged.  There is no charge on neutrons.

We should note the following points about the electrical charge:

1. The Coulomb is the large unit of charge. 1 Coulomb of charge consists of 6.24×10^18 electrons. i.e. (1/1.602×10^-19 ) = 6.24×10^18. That is why the value of charges are on the order of pC, nC or µC.
2. According to experimental observations, the charges that occur in nature are integral multiples of the electronic charge. i.e. 1e = -1.602×10^-19 C.
3. The law of conservation of charge states that “charge can neither be created nor destroyed but only transferred.” Thus the total sum of electrical charge in a system does not change.

The Coulomb is the large unit of charge. 1 Coulomb of charge consists of 6.24×10^18 electrons. i.e. (1/1.602×10^-19 ) = 6.24×10^18. That is why the value of charges are on the order of pC, nC or µC.

According to experimental observations, the charges that occur in nature are integral multiples of the electronic charge. i.e. 1e = -1.602×10^-19 C.
The law of conservation of charge states that “charge can neither be created nor destroyed but only transferred.” Thus the total sum of electrical charge in a system does not change.

## Coulomb’s Law

Coulomb’s law states that:

“The force of attraction or repulsion between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance present between them”

Suppose consider two point charges q2 and q1 that separates by a distance of R in a vacuum. The force by q on q2  will be: Where K is the proportionality constant.

The value of proportionality constant (Kcan be determined as: The direction of the charge movement is determined by the property of charged particles. If both are charged particles are of the same type, they will repel each other and vice versa.

## Electric Current

We now consider the flow of electric charge. Any movement of charge constitutes an electric current. These charge carriers could be electrons in a vacuum or metals, holes in a semiconductor or ions in a solution when we connect a conducting wire to a battery, the charges within the wire moves. The positive charge particles move in one direction while the negative charge particles move in the opposite direction. This motion of charged particles creates an electric current. Thus, electrical current can be defined as:

“Electric current is the time rate of change of charge, measured in Amperes (A)”

It is conventional to take the direction of electric current flow as the movement of positive charges. This conventional current concept was introduced by Benjamin Franklin is also known as the inventor of electricity. Although we know that flow of electric current in the metallic conductor is due to electron movements which are negatively charged, but we have to follow the universal convention of electrical current that current flow is due to net positive charges.

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