The concept of electric charge and current is the underlying principle for explaining all electrical phenomena. Without a good knowledge of this concept, it will be hard to learn basic electrical engineering. This article helps you to understand the concept and relationship between charge and current.
Definition of Charge and Current
Electric charge is an electrical property of the atomic particles of which matter consists, measured in coulombs (C).
Electric current is the time rate of change of charge, measured in amperes (A).
The most important difference between the charge and current is that the charge is the physical property of matter, whereas the current is the rate of flow of charges.
The most basic quantity in an electric circuit is the electric charge.
We all experience the effect of electric charge when we try to remove our wool sweater and have it stick to our body. Another one is when we walk across a carpet and receive a shock.
We already discussed the structure of an atom in electrical engineering basics. There we studied that matter is made of fundamental building blocks known as atoms and that each atom consists of electrons, protons, and neutrons.
We also know that the charge e on an electron is negative and equal in magnitude to 1.602 × 10−19 C, while a proton carries a positive charge of the same magnitude as the electron.
The presence of equal numbers of protons and electrons leaves an atom neutrally charged.
The following points should be noted about electric charge:
- A coulomb is a large unit for charges.
- In 1 C of charge, there are 1∕(1.602 × 10−19) = 6.24 × 1018 electrons.
- Thus realistic or laboratory values of charges are on the order of pC, nC, or μC.
- According to experimental observations, the only charges that occur in nature are integral multiples of the electronic charge e = −1.602 × 10−19 C.
- The law of conservation of charge states that charge can neither be created nor destroyed, only transferred.
- Thus, the algebraic sum of the electric charges in a system does not change.
Relationship between charge and current
In order to understand the relationship between charge and current, we should consider the flow of electric charges.
A unique feature of electric charge or electricity is the fact that it is mobile. That means it can be transferred from one place to another, where it can be converted to another form of energy.